Dual core golf ball having positive-hardness-gradient thermoplastic inner core and positive-hardness-gradient thermoset outer core layer

ABSTRACT

A golf ball includes a thermoplastic inner core and a thermoset outer core layer. The inner core has a surface hardness of about 40 to 80 Shore C and a center hardness of about 30 to 75 Shore C, the center hardness being less than the surface hardness to define a first positive hardness gradient. The cover includes an inner cover layer and an outer cover layer. The thermoplastic inner core comprises a highly-neutralized ionomer including an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid; a plasticizer; an organic acid or salt thereof; and a cation source present in an amount sufficient to neutralize from about 70 to 100% of the acid groups present. The outer core layer includes a polybutadiene rubber and has a surface hardness greater than an interior hardness to define a positive hardness gradient of less than about 25 Shore C

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/578,787, filed Dec. 22, 2014, which is a continuation-in-part ofco-pending U.S. patent application Ser. No. 14/282,229, filed May 20,2014 and now U.S. Pat. No. 9,149,689, which is a continuation-in-part ofU.S. patent application Ser. No. 13/477,344, filed May 22, 2012 and nowU.S. Pat. No. 8,727,912, which is a continuation of U.S. patentapplication Ser. No. 13/036,642, filed Feb. 28, 2011 and now abandoned,which is a continuation of U.S. patent application Ser. No. 12/342,545,filed Dec. 23, 2008 and now U.S. Pat. No. 7,946,934, which is acontinuation-in-part of U.S. patent application Ser. No. 12/339,495,filed Dec. 19, 2008 and now U.S. Pat. No. 7,815,526, which is acontinuation-in-part of U.S. patent application Ser. No. 12/196,522,filed Aug. 22, 2008 and now U.S. Pat. No. 7,582,025, which is acontinuation of U.S. patent application Ser. No. 11/939,635, filed Nov.14, 2007 and now U.S. Pat. No. 7,427,242, the disclosures of which areincorporated herein by reference thereto.

FIELD OF THE INVENTION

This invention relates generally to golf balls with cores, moreparticularly thermoplastic cores, having a surface hardness less thanthe center hardness to define a “negative” hardness gradient.

BACKGROUND OF THE INVENTION

Solid golf balls are typically made with a solid core encased by acover, both of which can have multiple layers, such as a dual corehaving a solid center (or inner core) and an outer core layer, or amulti-layer cover having inner and outer cover layers. Generally, golfball cores and/or centers are constructed with a thermoset rubber, suchas a polybutadiene-based composition.

Thermoset polymers, once formed, cannot be reprocessed because themolecular chains are covalently bonded to one another to form athree-dimensional (non-linear) crosslinked network. The physicalproperties of the uncrosslinked polymer (pre-cure) are dramaticallydifferent than the physical properties of the crosslinked polymer(post-cure). For the polymer chains to move, covalent bonds would needto be broken—this is only achieved via degradation of the polymerresulting in dramatic loss of physical properties.

Thermoset rubbers are heated and crosslinked in a variety of processingsteps to create a golf ball core having certain desirablecharacteristics, such as higher or lower compression or hardness, thatcan impact the spin rate of the ball and/or provide better “feel.” Theseand other characteristics can be tailored to the needs of golfers ofdifferent abilities. Due to the nature of thermoset materials and theheating/curing cycles used to form them into cores, manufacturers canachieve varying properties across the core (i.e., from the core surfaceto the center of the core). For example, most conventional single coregolf ball cores have a ‘hard-to-soft’ hardness gradient from the surfaceof the core towards the center of the core.

In a conventional, polybutadiene-based core, the physical properties ofthe molded core are highly dependent on the curing cycle (i.e., the timeand temperature that the core is subjected to during molding). Thistime/temperature history, in turn, is inherently variable throughout thecore, with the center of the core being exposed to a differenttime/temperature (i.e., shorter time at a different temperature) thanthe surface (because of the time it takes to get heat to the center ofthe core) allowing a property gradient to exist at points between thecenter and core surface. This physical property gradient is readilymeasured as a hardness gradient, with a typical range of 5 to 40 ShoreC, and more commonly 10 to 30 Shore C, being present in virtually allgolf ball cores made from about the year 1970 on.

The patent literature contains a number of references that discuss‘hard-to-soft’ hardness gradients across a thermoset golf ball core.Additionally, a number of patents disclose multilayer thermoset golfball cores, where each core layer has a different hardness in an attemptto artificially create a hardness ‘gradient’ between core layer and corelayer. Because of the melt properties of thermoplastic materials,however, the ability to achieve varied properties across a golf ballcore has not been possible.

Unlike thermoset materials, thermoplastic polymers can be heated andre-formed, repeatedly, with little or no change in physical properties.For example, when at least the crystalline portion of a high molecularweight polymer is softened and/or melted (allowing for flow andformability), then cooled, the initial (pre-melting) and final(post-melting) molecular weights are essentially the same. The structureof thermoplastic polymers are generally linear, or slightly branched,and there is no intermolecular crosslinking or covalent bonding, therebylending these polymers their thermolabile characteristics. Therefore,with a thermoplastic core, the physical properties pre-molding areeffectively the same as the physical properties post-molding.Time/temperature variations have essentially no effect on the physicalproperties of a thermoplastic polymer.

As such, there is a need for a golf ball core, in particular a dualcore, that has a gradient from the surface to the center. The gradientmay be either soft-to-hard (a “negative” gradient), hard-to-soft (a“positive” gradient), or, in the case of a dual core having athermoplastic inner core layer, a combination of both gradients. A coreexhibiting such characteristics would allow the golf ball designer tocreate a thermoplastic core golf ball with unique gradient propertiesallowing for differences in ball characteristics such as compression,“feel,” and spin.

SUMMARY OF THE INVENTION

The present invention is directed to a golf ball including an inner corelayer consisting essentially of a thermoplastic material and having ageometric center hardness greater than a surface hardness to define anegative hardness gradient; an outer core layer disposed about the innercore, the outer core being formed from a substantially homogenousthermoset composition and having an inner surface hardness less than anouter surface hardness to define a positive hardness gradient; an innercover layer disposed outer core layer; and an outer cover layer disposedabout the inner cover layer, wherein the negative hardness gradient isfrom −1 to −5 Shore C, the positive hardness gradient is less than 25Shore C, and a difference between the inner core surface hardness andthe outer core inner surface hardness, Δh, is less than 25 Shore C.

In one embodiment, the thermoplastic material includes an ionomer, ahighly-neutralized ionomer, a thermoplastic polyurethane, athermoplastic polyurea, a styrene block copolymer, a polyester amide,polyester ether, a polyethylene acrylic acid copolymer or terpolymer, ora polyethylene methacrylic acid copolymer or terpolymer.

Preferably, the difference between the inner core surface hardness andthe outer core inner surface hardness, Δh, is less than Shore C, morepreferably less than 15 Shore C. The inner core center hardness shouldbe about 90 Shore C to about 100 Shore C. The inner core surfacehardness should be about 85 Shore C to about 95 Shore C. The hardness ofthe inner surface of the outer core layer should be about 65 Shore C toabout 75 Shore C. The hardness of the outer surface of the outer corelayer should be about 80 Shore C to about 90 Shore C.

Preferably, the outer core layer includes diene rubber and a metal saltof a carboxylic acid in an amount of about 25 phr to about 40 phr. Inone particular embodiment, hardness of the inner surface of the outercore layer and the hardness of the outer surface of the outer core layerare both less than the hardness of the outer surface of the inner core.Optionally, the outer core layer includes a soft and fast agent.

The present invention is also directed to a golf ball including an innercore layer consisting of a thermoplastic material and having a geometriccenter hardness greater than a surface hardness to define a negativehardness gradient between −1 Shore C and −5 Shore C; an outer core layerdisposed about the inner core, the outer core being formed from asubstantially homogenous thermoset composition comprising a diene rubberand having an inner surface hardness less than an outer surface hardnessto define a positive hardness gradient of less than 25 Shore C; a coverlayer disposed outer core layer, the cover layer comprising an innercover layer comprising an ionomer and an outer cover layer comprising acastable polyurethane or polyurea material, wherein a difference betweenthe inner core surface hardness and the outer core inner surfacehardness, Δh, is less than 20 Shore C.

The present invention is further directed to a golf ball including aninner core layer consisting of a thermoplastic material and having ageometric center hardness greater than a surface hardness to define anegative hardness gradient between −1 Shore C and −5 Shore C, the centerhardness being about 90 Shore C to about 100 Shore C and the surfacehardness being about 85 Shore C to about 95 Shore C; an outer core layerdisposed about the inner core, the outer core being formed from asubstantially homogenous thermoset composition comprising a diene rubberand having an inner surface hardness less than an outer surface hardnessto define a positive hardness gradient of less than 25 Shore C, theinner surface being about 65 Shore C to about 75 Shore C and the surfacebeing about 80 Shore C to about 90 Shore C; a cover layer disposed outercore layer, the cover layer comprising an inner cover layer comprisingan ionomer and an outer cover layer comprising a castable polyurethaneor polyurea material, wherein a difference between the inner coresurface hardness and the outer core inner surface hardness, Δh, is lessthan 20 Shore C.

The present invention is directed to a golf ball having a core includinga thermoplastic inner core and a thermoset outer core layer. The innercore has a surface hardness of about 40 to 80 Shore C and a centerhardness of about 30 to 75 Shore C. The center hardness of the innercore is less than the surface hardness of the inner core so that it hasa positive hardness gradient. A cover layer is formed over the core. Thecover includes an inner cover layer and an outer cover layer. Thethermoplastic inner core includes a highly-neutralized ionomercomprising a copolymer of ethylene and an α,β-unsaturated carboxylicacid, an organic acid or salt thereof, and sufficient cation source toneutralize the acid groups of the copolymer by 80% or greater. The outercore layer includes a polybutadiene rubber and has a positive hardnessgradient of less than 25 Shore C.

In one embodiment, the thermoplastic inner core further includes anethylene/acid copolymer or ionomer. Preferably, the positive hardnessgradient is 1 to 15 Shore C. In another embodiment, the acid groups ofthe copolymer are neutralized by 90% or greater. The organic acid orsalt thereof may include barium, lithium, sodium, zinc, bismuth,chromium, cobalt, copper, potassium, strontium, titanium, tungsten,magnesium, cesium, iron, nickel, silver, aluminum, tin, or calciumsalts, or, additionally, the salts of fatty acids. In this case, thefatty acid salt includes stearic acid, behenic acid, erucic acid, oleicacid, linoelic acid or dimerized derivatives thereof. Preferably, theorganic acid or salt thereof comprises a magnesium salt of oleic acid.

In an alternative embodiment, the acid copolymer further includes asoftening comonomer. The highly-neutralized ionomer may also furtherinclude a second polymer component, such as ionomeric copolymers andterpolymers, ionomer precursors, thermoplastics, polyamides,polycarbonates, polyesters, polyurethanes, polyureas, thermoplasticelastomers, polybutadiene rubber, balata, grafted- or non-graftedmetallocene-catalyzed polymers, single-site polymers, high-crystallineacid polymers, or cationic ionomers.

The present invention is also directed to a golf ball having a coreincluding a thermoplastic inner core and a thermoset outer core layer.The inner core has a surface hardness of about 60 to 90 Shore C and acenter hardness of about 65 to 95 Shore C. The center hardness is lessthan the surface hardness such that the inner core layer has a positivehardness gradient. A cover is formed around the core and includes aninner cover layer and an outer cover layer. The thermoplastic inner coreincludes a highly-neutralized ionomer comprising a copolymer of ethyleneand an α,β-unsaturated carboxylic acid, an organic acid or salt thereof,and sufficient cation source to neutralize the acid groups of thecopolymer by 80% or greater. The outer core layer includes apolybutadiene rubber and has a surface hardness greater than an interiorhardness such that the outer core layer has a positive hardness gradientof less than 25 Shore C.

The present invention is directed to a golf ball includes athermoplastic inner core and a thermoset outer core layer. The innercore has a surface hardness of about 40 to 80 Shore C and a centerhardness of about 30 to 75 Shore C, the center hardness being less thanthe surface hardness to define a first positive hardness gradient. Thecover includes an inner cover layer and an outer cover layer. Thethermoplastic inner core comprises a highly-neutralized ionomerincluding an acid copolymer of ethylene and an α,β-unsaturatedcarboxylic acid; a plasticizer; an organic acid or salt thereof; and acation source present in an amount sufficient to neutralize from about70 to 100% of the acid groups present. The outer core layer includes apolybutadiene rubber and has a surface hardness greater than an interiorhardness to define a positive hardness gradient of less than about 25Shore C.

The thermoplastic inner core may further include an ethylene/acidcopolymer or ionomer.

In one embodiment, the positive hardness gradient is 1 to 15 Shore C.The acid groups of the copolymer are preferably neutralized by 90% orgreater, more preferably about 100%. The organic acid or salt thereofincludes barium, lithium, sodium, zinc, bismuth, chromium, cobalt,copper, potassium, strontium, titanium, tungsten, magnesium, cesium,iron, nickel, silver, aluminum, tin, or calcium salts, or salts of fattyacids. The fatty acid salt includes stearic acid, behenic acid, erucicacid, oleic acid, linoelic acid or dimerized derivatives thereof.Preferably, the organic acid or salt thereof includes a magnesium saltof oleic acid.

The acid copolymer may further include a softening comonomer and/or thehighly-neutralized ionomer may include a second polymer component, suchas ionomeric copolymers and terpolymers, ionomer precursors,thermoplastics, polyamides, polycarbonates, polyesters, polyurethanes,polyureas, thermoplastic elastomers, polybutadiene rubber, balata,grafted- or non-grafted metallocene-catalyzed polymers, single-sitepolymers, high-crystalline acid polymers, or cationic ionomers.

The present invention is also directed to a golf ball having athermoplastic inner core and a thermoset outer core layer. The innercore has a surface hardness of about 60 to 90 Shore C and a centerhardness of about 65 to 95 Shore C. The center hardness is less than thesurface hardness to define a positive hardness gradient. The coverincludes an inner cover layer and an outer cover layer. Thethermoplastic inner core includes a highly-neutralized ionomer formedfrom an acid copolymer of ethylene and an α,β-unsaturated carboxylicacid, an optional softening monomer such as alkyl acrylate ormethacrylate, a plasticizer; an organic acid or salt thereof; and acation source present in an amount sufficient to neutralize from about70 to about 100% of all acid groups present in the composition. Theouter core layer includes a polybutadiene rubber and has a surfacehardness greater than the interior hardness to define a positivehardness gradient of less than about 25 Shore C.

The thermoplastic inner core may include an ethylene/acid copolymer orionomer. In one embodiment, the positive hardness gradient is 1 to 15Shore C. The acid groups of the copolymer are preferably neutralized by90% or greater, more preferably about 100%. The organic acid or saltthereof can be barium, lithium, sodium, zinc, bismuth, chromium, cobalt,copper, potassium, strontium, titanium, tungsten, magnesium, cesium,iron, nickel, silver, aluminum, tin, or calcium salts, or salts of fattyacids. The fatty acid salt can be stearic acid, behenic acid, erucicacid, oleic acid, linoelic acid or dimerized derivatives thereof.Preferably, the organic acid or salt thereof is a magnesium salt ofoleic acid. The acid copolymer may include an optional softeningcomonomer and/or the highly-neutralized ionomer may include a secondpolymer component, such as ionomeric copolymers and terpolymers, ionomerprecursors, thermoplastics, polyamides, polycarbonates, polyesters,polyurethanes, polyureas, thermoplastic elastomers, polybutadienerubber, balata, grafted- or non-grafted metallocene-catalyzed polymers,single-site polymers, high-crystalline acid polymers, or cationicionomers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing preferred hardness values and relationshipsbetween the “negative” hardness gradient thermoplastic inner core layerand the steep “positive” hardness gradient thermoset outer core layer ofthe present invention;

FIG. 2 is a graph showing preferred hardness values and relationshipsbetween the “negative” hardness gradient thermoplastic inner core layerand the conventional “positive” hardness gradient thermoset outer corelayer of the present invention; and

FIG. 3 is one embodiment of a golf ball of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The golf balls of the present invention may include a single-layer(one-piece) golf ball, and multi-layer golf balls, such as one having acore and a cover surrounding the core, but are preferably formed from acore comprised of a solid center (otherwise known as an inner corelayer) and an outer core layer, and a cover layer. Of course, any of thecore and/or the cover layers may include more than one layer. In apreferred embodiment, the core is formed of a thermoplastic inner corelayer and a rubber-based outer core layer where the inner core has a“soft-to-hard” hardness gradient (a “negative” hardness gradient) asmeasured radially inward from the outer surface and the outer core layerhas a “hard-to-soft” hardness gradient (a “positive” hardness gradient)as measured radially inward from the outer core outer surface.

The inventive cores may have a hardness gradient defined by hardnessmeasurements made at the surface of the inner core (or outer core layer)and at points radially inward towards the center of the inner core,typically at 2-mm increments. As used herein, the terms “negative” and“positive” hardness gradients refer to the result of subtracting thehardness value at the innermost portion of the component being measured(e.g., the center of a solid core or an inner core in a dual coreconstruction; the inner surface of a core layer; etc.) from the hardnessvalue at the outer surface of the component being measured (e.g., theouter surface of a solid core; the outer surface of an inner core in adual core; the outer surface of an outer core layer in a dual core,etc.). For example, if the outer surface of a solid core has a lowerhardness value than the center (i.e., the surface is softer than thecenter), the hardness gradient will be deemed a “negative” gradient (asmaller number−a larger number=a negative number).

In a preferred embodiment, the golf balls of the present inventioninclude an inner core layer formed from a thermoplastic (TP) material todefine a “negative” hardness gradient and an outer core layer formedfrom a thermoset (TS) material to define a shallow (less than 25 Shore Cpoints) “positive” hardness gradient. The TP hardness gradient may becreated by exposing the cores to a high-energy radiation treatment, suchas electron beam or gamma radiation, such as disclosed in U.S. Pat. No.5,891,973, which is incorporated by reference thereto, or lower energyradiation, such as UV or IR radiation; a solution treatment, such as ina isocyanate, silane, plasticizer, or amine solution, such as suitableamines disclosed in U.S. Pat. No. 4,732,944, which is incorporated byreference thereto; incorporation of additional free radical initiatorgroups in the TP prior to molding; chemical degradation; and/or chemicalmodification, to name a few. The magnitude of the “negative” hardnessgradient is preferably greater than (more negative) −1 Shore C, morepreferably greater than −3 Shore C, and most preferably greater than −5Shore C. In one specific embodiment, the magnitude of the “negative”hardness gradient is −1 to −5.

Preferably, the core or core layers (inner core or outer core layer),most preferably the inner core layer, are formed from a compositionincluding at least one thermoplastic material. Preferably, thethermoplastic material comprises highly neutralized polymers;ethylene/acid copolymers and ionomers; ethylene/(meth)acrylateester/acid copolymers and ionomers; ethylene/vinyl acetates;polyetheresters; polyetheramides; thermoplastic polyurethanes;metallocene catalyzed polyolefins; polyalkyl(meth)acrylates;polycarbonates; polyamides; polyamide-imides; polyacetals; polyethylenes(i.e., LDPE, HDPE, UHMWPE); high impact polystyrenes;acrylonitrile-butadiene-styrene copolymers; polyesters; polypropylenes;polyvinyl chlorides; polyetheretherketones; polyetherimides;polyethersulfones; polyimides; polymethylpentenes; polystyrenes;polysulfones; or mixtures thereof. In a more preferred embodiment, thethermoplastic material is a highly-neutralized polymer, preferably afully-neutralized ionomer. Other suitable thermoplastic materials aredisclosed in U.S. Pat. Nos. 6,213,895 and 7,147,578, which areincorporated herein by reference thereto.

In a preferred embodiment, the inner core layer is formed from an HNPmaterial or a blend of HNP materials. The acid moieties of the HNP's,typically ethylene-based ionomers, are preferably neutralized greaterthan about 70%, more preferably greater than about 90%, and mostpreferably at least about 100%. The HNP's can be also be blended with asecond polymer component, which, if containing an acid group, may beneutralized in a conventional manner, by the organic fatty acids of thepresent invention, or both. The second polymer component, which may bepartially or fully neutralized, preferably comprises ionomericcopolymers and terpolymers, ionomer precursors, thermoplastics,polyamides, polycarbonates, polyesters, polyurethanes, polyureas,thermoplastic elastomers, polybutadiene rubber, balata,metallocene-catalyzed polymers (grafted and non-grafted), single-sitepolymers, high-crystalline acid polymers, cationic ionomers, and thelike. HNP polymers typically have a material hardness of between about20 and about 80 Shore D, and a flexural modulus of between about 3,000psi and about 200,000 psi.

In one embodiment of the present invention the HNP's are ionomers and/ortheir acid precursors that are preferably neutralized, either filly orpartially, with organic acid copolymers or the salts thereof. The acidcopolymers are preferably α-olefin, such as ethylene, C₃₋₈α,β-ethylenically unsaturated carboxylic acid, such as acrylic andmethacrylic acid, copolymers. They may optionally contain a softeningmonomer, such as alkyl acrylate and alkyl methacrylate, wherein thealkyl groups have from 1 to 8 carbon atoms.

The acid copolymers can be described as E/X/Y copolymers where E isethylene, X is an α,β-ethylenically unsaturated carboxylic acid, and Yis a softening comonomer. In a preferred embodiment, X is acrylic ormethacrylic acid and Y is a C₁₋₈ alkyl acrylate or methacrylate ester. Xis preferably present in an amount from about 1 to about 35 weightpercent of the polymer, more preferably from about 5 to about 30 weightpercent of the polymer, and most preferably from about 10 to about 20weight percent of the polymer. Y is preferably present in an amount fromabout 0 to about 50 weight percent of the polymer, more preferably fromabout 5 to about 25 weight percent of the polymer, and most preferablyfrom about 10 to about 20 weight percent of the polymer.

Specific acid-containing ethylene copolymers include, but are notlimited to, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylicacid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate,ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylicacid/n-butyl methacrylate, ethylene/acrylic acid/methyl methacrylate,ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/methacrylic acid/methyl methacrylate, andethylene/acrylic acid/n-butyl methacrylate. Preferred acid-containingethylene copolymers include, ethylene/methacrylic acid/n-butyl acrylate,ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/acrylic acid/ethyl acrylate, ethylene/methacrylicacid/ethyl acrylate, and ethylene/acrylic acid/methyl acrylatecopolymers. The most preferred acid-containing ethylene copolymers are,ethylene/(meth) acrylic acid/n-butyl, acrylate, ethylene/(meth)acrylicacid/ethyl acrylate, and ethylene/(meth) acrylic acid/methyl acrylatecopolymers.

Ionomers are typically neutralized with a metal cation, such as Li, Na,Mg, K, Ca, or Zn. It has been found that by adding sufficient organicacid or salt of organic acid, along with a suitable base, to the acidcopolymer or ionomer, however, the ionomer can be neutralized, withoutlosing processability, to a level much greater than for a metal cation.Preferably, the acid moieties are neutralized greater than about 80%,preferably from 90-100%, most preferably 100% without losingprocessability. This is accomplished by melt-blending an ethyleneα,β-ethylenically unsaturated carboxylic acid copolymer, for example,with an organic acid or a salt of organic acid, and adding a sufficientamount of a cation source to increase the level of neutralization of allthe acid moieties (including those in the acid copolymer and in theorganic acid) to greater than 90%, (preferably greater than 100%).

The organic acids of the present invention are aliphatic, mono- ormulti-functional (saturated, unsaturated, or multi-unsaturated) organicacids. Salts of these organic acids may also be employed. The salts oforganic acids of the present invention include the salts of barium,lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium,strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver,aluminum, tin, or calcium, salts of fatty acids, particularly stearic,behenic, erucic, oleic, linoelic or dimerized derivatives thereof. It ispreferred that the organic acids and salts of the present invention berelatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending).

The ionomers of the invention may also be more conventional ionomers,i.e., partially-neutralized with metal cations. The acid moiety in theacid copolymer is neutralized about 1 to about 90%, preferably at leastabout 20 to about 75%, and more preferably at least about 40 to about70%, to form an ionomer, by a cation such as lithium, sodium, potassium,magnesium, calcium, barium, lead, tin, zinc, aluminum, or a mixturethereof.

The highly neutralized polymer composition of the inner core layercomprises an acid copolymer, a non-acid polymer, an organic acid or saltthereof, and a cation source present in an amount sufficient toneutralize greater than 80% of all acid groups present in thecomposition. The acid copolymer is a copolymer of ethylene and anα,β-unsaturated carboxylic acid, optionally including a softeningmonomer selected from the group consisting of alkyl acrylates andmethacrylates. The non-acid polymer is selected from the groupconsisting of polyolefins, polyamides, polyesters, polyethers,polyurethanes, metallocene-catalyzed polymers, single-site catalystpolymerized polymers, ethylene propylene rubber, ethylene propylenediene rubber, styrenic block copolymer rubbers, alkyl acrylate rubbers,and functionalized derivatives thereof.

Set forth below are particularly suitable highly-neutralized polymercompositions for forming thermoplastic core layers. The followingcommercially-available materials were used in the below examples:

A-C® 5120 ethylene acrylic acid copolymer with an acrylic acid contentof 15%, A-C® 5180 ethylene acrylic acid copolymer with an acrylic acidcontent of 20%, A-C® 395 high density oxidized polyethylene homopolymer,and A-C® 575 ethylene maleic anhydride copolymer, commercially availablefrom Honeywell;

CB23 high-cis neodymium-catalyzed polybutadiene rubber, commerciallyavailable from Lanxess Corporation;

CA1700 Soya fatty acid, CA1726 linoleic acid, and CA1725 conjugatedlinoleic acid, commercially available from Chemical Associates; Century®1107 highly purified isostearic acid mixture of branched andstraight-chain C18 fatty acid, commercially available from ArizonaChemical;

Clarix® 011370-01 ethylene acrylic acid copolymer with an acrylic acidcontent of 13% and Clarix® 011536-01 ethylene acrylic acid copolymerwith an acrylic acid content of 15%, commercially available from A.Schulman Inc.;

Elvaloy® AC 1224 ethylene-methyl acrylate copolymer with a methylacrylate content of 24 wt %, Elvaloy® AC 1335 ethylene-methyl acrylatecopolymer with a methyl acrylate content of 35 wt %, Elvaloy® AC 2116ethylene-ethyl acrylate copolymer with an ethyl acrylate content of 16wt %, Elvaloy® AC 3427 ethylene-butyl acrylate copolymer having a butylacrylate content of 27 wt %, and Elvaloy® AC 34035 ethylene-butylacrylate copolymer having a butyl acrylate content of 35 wt %,commercially available from E.I. Dupont de Nemours and Company;

Escor® AT-320 ethylene acid terpolymer, commercially available fromExxonMobil Chemical Company;

Exxelor® VA 1803 amorphous ethylene copolymer functionalized with maleicanhydride, commercially available from ExxonMobil Chemical Company;Fusabond® N525 metallocene-catalyzed polyethylene, Fusabond® N416chemically modified ethylene elastomer, Fusabond® C190 anhydridemodified ethylene vinyl acetate copolymer, and Fusabond® P614functionalized polypropylene, commercially available from E.I. Dupont deNemours and Company;

Hytrel® 3078 very low modulus thermoplastic polyester elastomer,commercially available from E.I. Dupont de Nemours and Company;

Kraton® FG 1901 GT linear triblock copolymer based on styrene andethylene/butylene with a polystyrene content of 30% and Kraton® FG1924GTlinear triblock copolymer based on styrene and ethylene/butylene with apolystyrene content of 13%, commercially available from KratonPerformance Polymers Inc.;

Lotader® 4603, 4700 and 4720, random copolymers of ethylene, acrylicester and maleic anhydride, commercially available from ArkemaCorporation;

Nordel® IP 4770 high molecular weight semi-crystalline EPDM rubber,commercially available from The Dow Chemical Company;

Nucrel® 9-1, Nucrel® 599, Nucrel® 960, Nucrel® 0407, Nucrel® 0609,Nucrel® 1214, Nucrel® 2906, Nucrel® 2940, Nucrel® 30707, Nucrel® 31001,and Nucrel® AE acid copolymers, commercially available from E.I. Dupontde Nemours and Company;

Primacor® 3150, 3330, 5980I, and 5990I acid copolymers, commerciallyavailable from The Dow Chemical Company;

Royaltuf® 498 maleic anhydride modified polyolefin based on an amorphousEPDM, commercially available from Chemtura Corporation;

Sylfat® FA2 tall oil fatty acid, commercially available from ArizonaChemical;

Vamac® G terpolymer of ethylene, methylacrylate and a cure site monomer,commercially available from E.I. Dupont de Nemours and Company; and

XUS 60758.08L ethylene acrylic acid copolymer with an acrylic acidcontent of 13.5%, commercially available from The Dow Chemical Company.

Various compositions were melt blended using components as given inTable 18 below. The compositions were neutralized by adding a cationsource in an amount sufficient to neutralize, theoretically, 110% of theacid groups present in components 1 and 3, except for example 72, inwhich the cation source was added in an amount sufficient to neutralize75% of the acid groups. Magnesium hydroxide was used as the cationsource, except for example 68, in which magnesium hydroxide and sodiumhydroxide were used in an equivalent ratio of 4:1. In addition tocomponents 1-3 and the cation source, example 71 contains ethyl oleateplasticizer.

The relative amounts of component 1 and component 2 used are indicatedin Table 18 below, and are reported in wt %, based on the combinedweight of components 1 and 2. The relative amounts of component 3 usedare indicated in Table 1 below, and are reported in wt %, based on thetotal weight of the composition.

TABLE 1 Ex. Component 1 wt % Component 2 wt % Component 3 wt % 1Primacor 5980I 78 Lotader 4603 22 magnesium oleate 41.6 2 Primacor 5980I84 Elvaloy AC 1335 16 magnesium oleate 41.6 3 Primacor 5980I 78 ElvaloyAC 3427 22 magnesium oleate 41.6 4 Primacor 5980I 78 Elvaloy AC 1335 22magnesium oleate 41.6 5 Primacor 5980I 78 Elvaloy AC 1224 22 magnesiumoleate 41.6 6 Primacor 5980I 78 Lotader 4720 22 magnesium oleate 41.6 7Primacor 5980I 85 Vamac G 15 magnesium oleate 41.6 8 Primacor 5980I 90Vamac G 10 magnesium oleate 41.6 8.1 Primacor 5990I 90 Fusabond 614 10magnesium oleate 41.6 9 Primacor 5980I 78 Vamac G 22 magnesium oleate41.6 10 Primacor 5980I 75 Lotader 4720 25 magnesium oleate 41.6 11Primacor 5980I 55 Elvaloy AC 3427 45 magnesium oleate 41.6 12 Primacor5980I 55 Elvaloy AC 1335 45 magnesium oleate 41.6 12.1 Primacor 5980I 55Elvaloy AC 34035 45 magnesium oleate 41.6 13 Primacor 5980I 55 ElvaloyAC 2116 45 magnesium oleate 41.6 14 Primacor 5980I 78 Elvaloy AC 3403522 magnesium oleate 41.6 14.1 Primacor 5990I 80 Elvaloy AC 34035 20magnesium oleate 41.6 15 Primacor 5980I 34 Elvaloy AC 34035 66 magnesiumoleate 41.6 16 Primacor 5980I 58 Vamac G 42 magnesium oleate 41.6 17Primacor 5990I 80 Fusabond 416 20 magnesium oleate 41.6 18 Primacor5980I 100 — — magnesium oleate 41.6 19 Primacor 5980I 78 Fusabond 416 22magnesium oleate 41.6 20 Primacor 5990I 100 — — magnesium oleate 41.6 21Primacor 5990I 20 Fusabond 416 80 magnesium oleate 41.6 21.1 Primacor5990I 20 Fusabond 416 80 magnesium oleate 31.2 21.2 Primacor 5990I 20Fusabond 416 80 magnesium oleate 20.8 22 Clarix 011370 30.7 Fusabond 41669.3 magnesium oleate 41.6 23 Primacor 5990I 20 Royaltuf 498 80magnesium oleate 41.6 24 Primacor 5990I 80 Royaltuf 498 20 magnesiumoleate 41.6 25 Primacor 5990I 80 Kraton FG1924GT 20 magnesium oleate41.6 26 Primacor 5990I 20 Kraton FG1924GT 80 magnesium oleate 41.6 27Nucrel 30707 57 Fusabond 416 43 magnesium oleate 41.6 28 Primacor 5990I80 Hytrel 3078 20 magnesium oleate 41.6 29 Primacor 5990I 20 Hytrel 307880 magnesium oleate 41.6 30 Primacor 5980I 26.8 Elvaloy AC 34035 73.2magnesium oleate 41.6 31 Primacor 5980I 26.8 Lotader 4603 73.2 magnesiumoleate 41.6 32 Primacor 5980I 26.8 Elvaloy AC 2116 73.2 magnesium oleate41.6 33 Escor AT-320 30 Elvaloy AC 34035 52 magnesium oleate 41.6Primacor 5980I 18 34 Nucrel 30707 78.5 Elvaloy AC 34035 21.5 magnesiumoleate 41.6 35 Nucrel 30707 78.5 Fusabond 416 21.5 magnesium oleate 41.636 Primacor 5980I 26.8 Fusabond 416 73.2 magnesium oleate 41.6 37Primacor 5980I 19.5 Fusabond N525 80.5 magnesium oleate 41.6 38 Clarix011536-01 26.5 Fusabond N525 73.5 magnesium oleate 41.6 39 Clarix011370-01 31 Fusabond N525 69 magnesium oleate 41.6 39.1 XUS 60758.08L29.5 Fusabond N525 70.5 magnesium oleate 41.6 40 Nucrel 31001 42.5Fusabond N525 57.5 magnesium oleate 41.6 41 Nucrel 30707 57.5 FusabondN525 42.5 magnesium oleate 41.6 42 Escor AT-320 66.5 Fusabond N525 33.5magnesium oleate 41.6 43 Nucrel 2906/2940 21 Fusabond N525 79 magnesiumoleate 41.6 44 Nucrel 960 26.5 Fusabond N525 73.5 magnesium oleate 41.645 Nucrel 1214 33 Fusabond N525 67 magnesium oleate 41.6 46 Nucrel 59940 Fusabond N525 60 magnesium oleate 41.6 47 Nucrel 9-1 44.5 FusabondN525 55.5 magnesium oleate 41.6 48 Nucrel 0609 67 Fusabond N525 33magnesium oleate 41.6 49 Nucrel 0407 100 — — magnesium oleate 41.6 50Primacor 5980I 90 Fusabond N525 10 magnesium oleate 41.6 51 Primacor5980I 80 Fusabond N525 20 magnesium oleate 41.6 52 Primacor 5980I 70Fusabond N525 30 magnesium oleate 41.6 53 Primacor 5980I 60 FusabondN525 40 magnesium oleate 41.6 54 Primacor 5980I 50 Fusabond N525 50magnesium oleate 41.6 55 Primacor 5980I 40 Fusabond N525 60 magnesiumoleate 41.6 56 Primacor 5980I 30 Fusabond N525 70 magnesium oleate 41.657 Primacor 5980I 20 Fusabond N525 80 magnesium oleate 41.6 58 Primacor5980I 10 Fusabond N525 90 magnesium oleate 41.6 59 — — Fusabond N525 100magnesium oleate 41.6 60 Nucrel 0609 40 Fusabond N525 20 magnesiumoleate 41.6 Nucrel 0407 40 61 Nucrel AE 100 — — magnesium oleate 41.6 62Primacor 5980I 30 Fusabond N525 70 CA1700 soya 41.6 fatty acid magnesiumsalt 63 Primacor 5980I 30 Fusabond N525 70 CA1726 linoleic acid 41.6magnesium salt 64 Primacor 5980I 30 Fusabond N525 70 CA1725 conjugated41.6 linoleic acid magnesium salt 65 Primacor 5980I 30 Fusabond N525 70Century 1107 41.6 isostearic acid magnesium salt 66 A-C 5120 73.3Lotader 4700 26.7 magnesium oleate 41.6 67 A-C 5120 73.3 Elvaloy 3403526.7 magnesium oleate 41.6 68 Primacor 5980I 78.3 Lotader 4700 21.7magnesium oleate 41.6 and sodium salt 69 Primacor 5980I 47 ElvaloyAC34035 13 — — A-C 5180 40 70 Primacor 5980I 30 Fusabond N525 70 SylfatFA2 41.6 magnesium salt 71 Primacor 5980I 30 Fusabond N525 70 magnesiumoleate 31.2 ethyl oleate 10 72 Primacor 5980I 80 Fusabond N525 20sebacic acid 41.6 magnesium salt 73 Primacor 5980I 60 — — — — A-C 518040 74 Primacor 5980I 78.3 — — magnesium oleate 41.6 A-C 575 21.7 75Primacor 5980I 78.3 Exxelor VA 1803 21.7 magnesium oleate 41.6 76Primacor 5980I 78.3 A-C 395 21.7 magnesium oleate 41.6 77 Primacor 5980I78.3 Fusabond C190 21.7 magnesium oleate 41.6 78 Primacor 5980I 30Kraton FG 1901 70 magnesium oleate 41.6 79 Primacor 5980I 30 Royaltuf498 70 magnesium oleate 41.6 80 A-C 5120 40 Fusabond N525 60 magnesiumoleate 41.6 81 Primacor 5980I 30 Fusabond N525 70 erucic acid 41.6magnesium salt 82 Primacor 5980I 30 CB23 70 magnesium oleate 41.6 83Primacor 5980I 30 Nordel IP 4770 70 magnesium oleate 41.6 84 Primacor5980I 48 Fusabond N525 20 magnesium oleate 41.6 A-C 5180 32 85 Nucrel2806 22.2 Fusabond N525 77.8 magnesium oleate 41.6 86 Primacor 3330 61.5Fusabond N525 38.5 magnesium oleate 41.6 87 Primacor 3330 45.5 FusabondN525 20 magnesium oleate 41.6 Primacor 3150 34.5 88 Primacor 3330 28.5 —— magnesium oleate 41.6 Primacor 3150 71.5 89 Primacor 3150 67 FusabondN525 33 magnesium oleate 41.6 90 Primacor 5980I 55 Elvaloy AC 34035 45magnesium oleate lt 31.2 ethyl oleate 10

Solid spheres of each composition were injection molded, and the solidsphere COR, compression, Shore D hardness, and Shore C hardness of theresulting spheres were measured after two weeks. The results arereported in Table 2 below.

TABLE 2 Solid Sphere Solid Sphere Solid Sphere Solid Sphere Ex. CORCompression Shore D Shore C 1 0.845 120 59.6 89.2 3 0.871 117 57.7 88.64 0.867 122 63.7 90.6 5 0.866 119 62.8 89.9 8.1 0.869 127 65.3 92.9 120.856 101 55.7 82.4 12.1 0.857 105 53.2 81.3 14 0.873 122 64.0 91.1 170.878 117 60.1 89.4 18 0.853 135 67.6 94.9 20 0.857 131 66.2 94.4 210.752 26 34.8 57.1 21.1 0.729 9 34.3 56.3 21.2 0.720 2 33.8 55.2 30 **66 42.7 65.5 31 0.730 67 45.6 68.8 32 ** 100 52.4 78.2 33 0.760 64 43.664.5 34 0.814 91 52.8 80.4 51 0.873 121 61.5 90.2 52 0.870 116 60.4 88.253 0.865 107 57.7 84.4 54 0.853 97 53.9 80.2 55 0.837 82 50.1 75.5 560.818 66 45.6 70.7 57 0.787 45 41.3 64.7 58 0.768 26 35.9 57.3 ** spherebroke during measurement

HNP compositions may be used to form any core layer in accordance withthe present invention. Suitable HNP compositions, which are plasticizedper this invention, comprise an HNP, a plasticizer, and, optionally, amelt-flow modifier, additive, and/or filler. For purposes of the presentdisclosure, “HNP” generally refers to an acid polymer or blend of acidpolymers in which about 80% or greater of the acid groups areneutralized. The HNPs are typically formed by reacting the acidcopolymer with a sufficient amount of cation source, optionally in thepresence of a high molecular weight organic acid or salt thereof, toneutralize the acid groups in the acid copolymer by about 80% orgreater, more preferably about 90% or greater, and most preferably about100%. The cation source may even be present in an amount sufficient toneutralize, in a stoichiometric sense, greater than 100% of the acidgroups, more preferably about 110% or greater, and most preferably about120% or greater, because the neutralization process is less thanperfectly efficient. The acid copolymer can be reacted with the optionalhigh molecular weight organic acid or salt thereof and the cation sourcesimultaneously, or the acid copolymer can be reacted with the optionalhigh molecular weight organic acid or salt thereof prior to the additionof the cation source. The resulting HNP composition is then introducedto a plasticizer by a variety of means, such as soaking, mixing,blending, and the like. Suitable plasticizers are described below.

Suitable acid polymers include, but are not limited to, copolymers of anα-olefin and a C₃-C₈ α,β-ethylenically unsaturated carboxylic acid. Theα-olefin is preferably selected from ethylene and propylene. The acid ispreferably (meth) acrylic acid, ethacrylic acid, maleic acid, crotonicacid, fumaric acid, or itaconic acid, with (meth) acrylic acid beingparticularly preferred. Preferred acid copolymers include, but are notlimited to, those wherein the α-olefin is ethylene, the acid is (meth)acrylic acid, and the optional softening monomer is selected from (meth)acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, methyl(meth) acrylate, and ethyl (meth) acrylate. Particularly preferred acidcopolymers include, but are not limited to, ethylene/(meth) acrylicacid/n-butyl acrylate, ethylene/(meth) acrylic acid/methyl acrylate, andethylene/(meth) acrylic acid/ethyl acrylate. The acid polymer can,optionally, include a softening monomer, preferably alkyl (meth)acrylate, wherein the alkyl groups have from 1 to 8 carbons.

Suitable acid copolymers for forming the HNPs also include acid polymersthat are already partially neutralized. Examples of suitable partiallyneutralized acid copolymers include, but are not limited to, SURLYN®ionomers, commercially available from Dupont; AClyn® ionomers,commercially available from Honeywell International Inc.; and IOTEK®ionomers, commercially available from ExxonMobil Chemical Company. Alsosuitable are HPF 1000 and HPF 2000, ionomeric materials commerciallyavailable from Dupont. In some embodiments, very low modulusionomer-type ethylene-acid copolymers are particularly suitable forforming the HNPs and include SURLYN® 6320, SURLYN® 8120, SURLYN® 8320,and SURLYN® 9320, also commercially available from Dupont.

The α-olefin is typically present in the acid copolymer in an amount ofabout 15 wt % or greater, based on the total weight of the acidcopolymer. More preferably, the α-olefin is typically present in theacid copolymer in an amount of about 25 wt % or greater, more preferablyabout 40 wt % or greater, and most preferably about 60 wt % or greaterThe acid is typically present in the acid copolymer in an amount ofabout 1 wt % to about 25 wt %, more preferably about 8 wt % to about 20wt %, most preferably about 10 wt % to about 19 wt %, based on the totalweight of the acid copolymer. The optional softening monomer istypically present in the acid copolymer in an amount of about 0 wt % toabout 50 wt %, more preferably about 5 wt % to about 35 wt %, mostpreferably about 11 wt % to about 25 wt %, based on the total weight ofthe acid copolymer.

Suitable cation sources include metal ions and compounds of alkalimetals, alkaline earth metals and transition metals; metal ions andcompounds of rare earth elements; and combinations thereof. Preferredcation sources are metal ions and compounds of magnesium, sodium,potassium, cesium, calcium, barium, manganese, copper, zinc, tin,lithium, and rare earth metals. The acid copolymer may be at leastpartially neutralized prior to addition of the cation source to form theHNPs.

Suitable high molecular weight organic acids include aliphatic organicacids, aromatic organic acids, saturated monofunctional organic acids,unsaturated monofunctional organic acids, multi-unsaturatedmonofunctional organic acids, and dimerized derivatives thereof.Particular examples of suitable organic acids include, but are notlimited to, caproic acid, caprylic acid, capric acid, lauric acid,stearic acid, behenic acid, erucic acid, oleic acid, linoleic acid,myristic acid, benzoic acid, palmitic acid, phenylacetic acid,naphthalenoic acid, dimerized derivatives thereof, and combinationsthereof. Salts of high molecular weight organic acids comprise thesalts, particularly the barium, lithium, sodium, zinc, bismuth,chromium, cobalt, copper, potassium, strontium, titanium, tungsten,magnesium, and calcium salts, of aliphatic organic acids, aromaticorganic acids, saturated monofunctional organic acids, unsaturatedmonofunctional organic acids, multi-unsaturated monofunctional organicacids, dimerized derivatives thereof, and combinations thereof. The HNPcompositions comprise an organic acid salt in an amount of about 20 phror greater, more preferably about 30 phr or greater, most preferablyabout 40 phr or greater.

The plasticized HNP compositions of the present invention are notlimited by any particular method or any particular equipment for makingthe compositions. Typically, the desired acid copolymers andplasticizers are fed into a melt extruder, such as a single or twinscrew extruder. Other suitable methods for incorporating the plasticizerinto the HNP compositions are described below. A suitable amount ofcation source is then added such that at least about 80%, preferablyabout 90%, or most preferably 100%, of all acid groups present areneutralized. The acid copolymer may be at least partially neutralizedprior to the above process.

The HNP ethylene acid copolymer compositions may contain one or moreplasticizers. The plasticizers that may be used in the ethylene acidcopolymer compositions of this invention include, for example,N-butylbenzenesulfonamide; N-ethylbenzenesulfonamide;N-propylbenzenesulfonamide; N-butyl-N-dodecylbenzenesulfonamide;N,N-dimethylbenzenesulfonamide; p-methylbenzenesulfonamide; o,p-toluenesulfonamide; p-toluene sulfonamide; 2-ethylhexyl-4-hydroxybenzoate;hexadecyl-4-hydroxybenzoate; 1-butyl-4-hydroxybenzoate; dioctylphthalate; diisodecyl phthalate; di-(2-ethylhexyl) adipate; andtri-(2-ethylhexyl) phosphate; and blends thereof.

Other suitable plasticizers include polytetramethylene ether glycol,available from BASF under the tradename, PolyTHF™ 250; propylenecarbonate, available from Huntsman Corp., under the tradename, JEFFSOL®PC; and/or dipropyleneglycol dibenzoate, available from Eastman Chemicalunder the tradename, BENZOFLEX® 284.

Plasticizers such as benzene mono-, di-, and tricarboxylic acid esters;phthalates such as bis(2-ethylhexyl) phthalate, diisononyl phthalate,di-n-butyl phthalate, butyl benzyl phthalate, diisodecyl phthalate,dioctyl phthalate, diisooctyl phthalate, diethyl phthalate, diisobutylphthalate, and di-n-hexyl phthalate, and blends thereof are alsosuitable. Terephthalates, such as dioctyl terephthalate and dinonylisophthalate may be used. Also appropriate are trimellitates such astrimethyl trimellitate,tri-(2-ethylhexyl) trimellitate,tri-(n-octyl,n-decyl) trimellitate, tri-(heptyl,nonyl) trimellitate,tri-n-octyl trimellitate; as well as benzoates, including:2-ethylhexyl-4-hydroxy benzoate, n-octyl benzoate, methyl benzoate, andethyl benzoate, and blends thereof.

Plasticizers may include alkyl diacid esters commonly based on C₄-C₁₂alkyl dicarboxylic acids such as adipic, sebacic, azelaic, and maleicacids, such as bis(2-ethylhexyl)adipate, dimethyl adipate, monomethyladipate, dioctyl adipate, dibutyl sebacate, dibutyl maleate, diisobutylmaleate, dioctyl sebacate, and blends thereof. Also, esters based onglycols, polyglycols and polyhydric alcohols such as poly(ethyleneglycol) mono- and di-esters, cyclohexanedimethanol esters, sorbitolderivatives; and triethylene glycol dihexanoate, diethylene glycoldi-2-ethylhexanoate, tetraethylene glycol diheptanoate, and ethyleneglycol dioleate, and blends thereof, may be used.

Fatty acid esters also may be used as plasticizers in the compositionsof this invention. Compounds such as stearic, oleic, ricinoleic,behenic, myristic, linoleic, palmitic, and lauric acid esters, salts,and mono- and bis-amides can be used. Ethyl oleate, butyl stearate,methyl acetylricinoleate, zinc oleate, ethylene bis-oleamide, andstearyl erucamide are suitable. Fatty alcohols and acetylated fattyalcohols are also suitable, as are carbonate esters such as propylenecarbonate and ethylene carbonate. Mixtures of any of the plasticizersdescribed herein also may be used in accordance with this invention. Ina particularly preferred version, the fatty acid ester is an alkyloleate selected from the group consisting of methyl, propyl, ethyl,butyl, octyl, and decyl oleates. For example, in one version, ethyloleate is used as the plasticizer. In another version, butyl oleate oroctyl oleate is used in the composition. Preferably, the plasticizer is2-ethyl hexyl oleate.

Glycerol-based esters such as soy-bean, tung, or linseed oils or theirepoxidized derivatives or blends thereof can also be used asplasticizers in the present invention, as can polymeric polyesterplasticizers formed from the esterification reaction of diacids anddiglycols as well as from the ring-opening polymerization reaction ofcaprolactones with diacids or diglycols. Citrate esters and acetylatedcitrate esters are also suitable. Glycerol mono-, di-, and tri-oleatesmay be used per this invention, and in one preferred embodiment,glycerol trioleate is used as the plasticizer.

Dicarboxylic acid molecules containing both a carboxylic acid ester anda carboxylic acid salt can perform suitably as plasticizers. Themagnesium salt of mono-methyl adipate and the zinc salt of mono-octylglutarate are two such examples for this invention. Tri- andtetra-carboxylic acid esters and salts can also be used.

Also envisioned as suitable plasticizers are organophosphate andorganosulfur compounds such as tricresyl phosphate, tributyl phosphate,octyldiphenyl phosphate, alkyl sulfonic acid phenyl esters; and blendsthereof; and sulfonamides such as N-ethyl toluenesulfonamide,N-(2-hydroxypropyl)benzene sulfonamide, N-(n-butyl) benzenesulfonamide. Furthermore, thioester and thioether variants of theplasticizer compounds mentioned above are suitable.

Non-ester plasticizers such as alcohols, polyhydric alcohols, glycols,polyglycols, and polyethers also are suitable materials forplasticization. Materials such as polytetramethylene ether glycol,poly(ethylene glycol), and poly(propylene glycol), oleyl alchohol, andcetyl alcohol can be used. Hydrocarbon compounds, both saturated andunsaturated, linear or cyclic can be used such as mineral oils,microcrystalline waxes, or low-molecular weight polybutadiene.Halogenated hydrocarbon compounds can also be used.

Other examples of plasticizers that may be used in the ethylene acidcopolymer composition of this invention includebutylbenzenesulphonamide, ethylhexyl para-hydroxybenzoate and decylhexylpara-hydroxybenzoate.

Esters and alkylamides such as phthalic acid esters including dimethylphthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate,di-2-ethylhexyl phthalate, di-n-octyl phthalate, diisodecyl phthalate,ditridecyl phthalate, dicyclohexyl phthalate, butylbenzyl phthalate,diisononyl phthalate, ethylphthalylethyl glycolate, butylphthalylbutylglycolate, diundecyl phthalate, and di-2-ethylhexyl tetrahydrophthalate,also may be used.

Sulphonamides such as N-butylbenzenesulphonamide,ethyltoluene-suiphonamide, N-cyclohexyltoluenesulphonamide,2-ethylhexyl-para-hydroxybenzoate, 2-decylhexyl-para-hydroxybenzoate,oligoethyleneoxytetrahydrofurfuryl alcohol, or oligoethyleneoxymalonate; esters of hydroxybenzoic acid; esters or ethers oftetrahydrofurfuryl alcohol, and esters of citric acid or hydroxymalonicacid; and these plasticizers are also suitable.

Sulfonamides also may be used in the present invention. Examples of suchsulfonamides include N-alkyl benzenesulfonamides and toluenesufonamides,particularly N-butylbenzenesulfonamide,N-(2-hydroxypropyl)benzenesulfonamide, N-ethyl-o-toluenesulfonamide,N-ethyl-p-toluenesulfonamide, o-toluenesulfonamide,p-toluenesulfonamide.

SYLFAT® FA2 is particularly preferred and is a tall oil fatty acid,commercially available from Arizona Chemical, as is VAMAC® G, aterpolymer of ethylene, methylacrylate and a cure site monomer,commercially available from Dupont.

As noted above, fatty acid esters are particularly preferredplasticizers in the present invention. It has been found that the fattyacid esters perform well as plasticizers in the ethylene acid copolymercomposition. The fatty acid esters have several advantageous properties.For example, the fatty acid esters are compatible with the ethylene acidcopolymers and they tend to blend uniformly and completely with the acidcopolymer. Also, the fatty acid esters tend to improve the resiliencyand/or compression of the composition as discussed further below. Theethylene acid copolymer/plasticizer compositions may contain otheringredients that do not materially affect the basic and novelcharacteristics of the composition. For example, mineral fillers may beadded as discussed above. In one particular embodiment, the compositionincludes an ethylene acid copolymer, cation source sufficient toneutralize at least 80% of the acid groups present in the composition,and plasticizer, particularly a fatty acid ester.

One method of preparing the fatty acid ester involves reacting the fattyacid or mixture of fatty acids with a corresponding alcohol. The alcoholcan be any alcohol including, but not limited to, linear, branched, andcyclic alcohols. The fatty acid ester is commonly a methyl, ethyl,propyl, butyl, octyl, or other alkyl ester of a carboxylic acid thatcontains from 4 to 30 carbon atoms. In the present invention, ethyl,butyl, octyl, and decyl esters and particularly ethyl oleate, butyloleate, and octyl oleate are preferred fatty acid esters because oftheir properties. The carboxylic acid may be saturated or unsaturated.Examples of suitable saturated carboxylic acids, that is, carboxylicacids in which the carbon atoms of the alkyl chain are connected bysingle bonds, include but are not limited to butyric acid; capric acid;lauric acid; myristic acid; palmitic acid; stearic acid; and behenicacid. Examples of suitable unsaturated carboxylic acids, that is, acarboxylic acid in which there is one or more double bonds between thecarbon atoms in the alkyl chain, include but are not limited to oleicacid; linoleic acid; linolenic acid; and erucic acid.

As discussed above, the ethylene acid copolymer compositions of thisinvention contain a plasticizer, which is believed to aid in thereduction of the glass transition temperature (Tg) of the composition.The glass transition temperature is a temperature below which a polymeris relatively brittle and above which it is rubber-like and is typicallymeasured with a differential scanning calorimeter. In addition tolowering the Tg, the plasticizer may also reduce the tans in thetemperature range above the Tg. A dynamic mechanical analyzer istypically used to measure tans. The plasticizer may also reduce thehardness of the composition when compared to the same non-plasticizedcomposition. The effects of adding a plasticizer to the ethylene acidcopolymer composition on Tg, flex modulus, hardness, and other physicalproperties are discussed below.

It is believed that the plasticizer should be added in a sufficientamount to the ethylene acid copolymer composition so there is asubstantial change in the stiffness and/or hardness of the ethylene acidcopolymer. Thus, although the concentration of plasticizer may be aslittle as 1 wt % to form some ethylene acid copolymer compositions perthis invention, it is preferred that the concentration be relativelygreater. For example, it is preferred that the concentration of theplasticizer be at least about 3 wt %. More particularly, it is preferredthat the plasticizer be present in an amount of about 10 wt % to about80 wt %, more preferably about 20 wt % to about 60 wt %, most preferablyabout 25 wt % to about 50 wt %.

It is also believed that adding the plasticizer to the ethylene acidcopolymer helps make the composition softer and more rubbery. Adding theplasticizers to the composition helps decrease the stiffness of thecomposition. That is, the plasticizer helps lower the flex modulus ofthe composition. The flex modulus can be determined in accordance withASTM D790 standard among other testing procedures. Thus, in oneembodiment, the first ethylene acid copolymer (containing ethylene acidcopolymer only) composition has a first flex modulus value and thesecond ethylene acid copolymer (containing ethylene acid copolymer andplasticizer) composition has a second flex modulus value, wherein thesecond flex modulus value is less than the first flex modulus by atleast about 1%, more preferably at least about 10%.

The first ethylene acid copolymer (containing ethylene acid copolymeronly) composition has a first Tg value and the second ethylene acidcopolymer (containing ethylene acid copolymer and plasticizer)composition has a second Tg value. The second Tg value is preferably atleast 1° less than the first Tg value; more preferably at least 10° lessthan the first Tg value.

In addition, introducing the specific plasticizers of this inventioninto the ethylene acid copolymer composition generally helps to reducethe compression and/or increase the COR of the composition (when moldedinto a solid sphere and tested) versus a non-plasticized composition(when molded into a solid sphere and tested.) Plasticized ethylene acidcopolymer compositions typically show compression values lower, or atmost equal to, non-plasticized compositions while the plasticizedcompositions display COR values that may be higher, or at the leastequal to, non-plasticized compositions. This effect is surprising,because in many conventional compositions, the compression of thecomposition increases as the COR increases. In some instancesplasticization of the composition might produce a slight reduction inthe COR while at the same time reducing the compression to a greaterextent, thereby providing an overall improvement to the compression/CORrelationship over the non-plasticized composition.

TABLE I Examples, HNP Only Solid Sphere Solid Sphere Solid Sphere SolidSphere Shore D Shore C Example COR Compression Hardness Hardness HPFAD1035* 0.822 63 41.7 70.0 HPF AD1035 0.782 35 35.6 59.6 Soft* HPF 2000*0.856 91 46.1 76.5 *acid copolymer ionomer resin, available from DuPont

TABLE II Examples, HNP With Plasticizers Solid Sphere Solid Sphere SolidSphere Solid Sphere Shore D Shore C Example COR Compression HardnessHardness HPF 2000 0.856 91 46.1 76.5 HPF 2000 with 0.839 68 37.9 68.810% EO HPF 2000 with 0.810 32 30.2 53.0 20% EO HPF 2000 with 0.768 −1222.7 39.4 30% EO HPF 2000: acid copolymer ionomer resin, available fromDupont EO: ethyl oleate (plasticizer)

The addition of a fatty acid ester plasticizer (ethyl oleate) to theHNPs makes them faster (i.e., exhibit a higher COR at a givencompression or a given hardness) compared to the native polymer (withoutplasticizer). This allows the creation of materials that are faster andsofter than commercially-available polymers. This is very important forgolf ball layers, where ball speed (i.e., COR) is needed for distance,but where feel (softness or low compression) is also highly desirable tomost golfers. The ability to make a softer, better feeling golf ballthat has higher COR than predicted is surprising and highly beneficial.

TABLE III Acid CoPolymer Compositions E1 E2 E3 E4 CE1 CE2 CompositionHPF 2000 80 100 Primacor 5980i 16.5 39.7 38.6 18.3 Elvaloy 1335AC 11Fusabond N525 34.2 9.9 38.1 Oelic Acid 33.9 33 33.1 37.6 Magnesium 5.47.4 7.3 6.0 Hydroxide Ethyl Oleate 20 10 10 10 Properties Compression 3231 116 116 91 135 Shore C 53.0 60.2 83.7 81.5 76.5 90.2 Shore D 30.234.3 53.0 53.3 46.1 61.5 CoR at 125 ft/s 0.81 0.783 0.876 0.866 0.8560.873

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90° to this orientationprior to securing. A measurement is also made from the bottom of theholder to the top of the core to provide a reference point for futurecalculations. A rough cut is made slightly above the exposed geometriccenter of the core using a band saw or other appropriate cutting tool,making sure that the core does not move in the holder during this step.The remainder of the core, still in the holder, is secured to the baseplate of a surface grinding machine. The exposed ‘rough’ surface isground to a smooth, flat surface, revealing the geometric center of thecore, which can be verified by measuring the height from the bottom ofthe holder to the exposed surface of the core, making sure that exactlyhalf of the original height of the core, as measured above, has beenremoved to within 0.004 inches. Leaving the core in the holder, thecenter of the core is found with a center square and carefully markedand the hardness is measured at the center mark according to ASTMD-2240. Additional hardness measurements at any distance from the centerof the core can then be made by drawing a line radially outward from thecenter mark, and measuring the hardness at any given distance along theline, typically in 2-mm increments from the center. The hardness at aparticular distance from the center should be measured along at leasttwo, preferably four, radial arms located 180° apart, or 90° apart,respectively, and then averaged. All hardness measurements performed ona plane passing through the geometric center are performed while thecore is still in the holder and without having disturbed itsorientation, such that the test surface is constantly parallel to thebottom of the holder, and thus also parallel to the properly alignedfoot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball sub-assembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements and is set to record the maximumhardness reading attained for each measurement. The digital durometermust be attached to, and its foot made parallel to, the base of anautomatic stand. The weight on the durometer and attack rate conforms toASTM D-2240.

The direction of the hardness gradient of a golf ball layer is definedby the difference in hardness measurements taken at the outer and innersurfaces of a particular layer. The center hardness of an inner core andhardness of the outer surface of an inner core in a single-core ball orouter core layer are readily determined according to the test proceduresprovided above. The outer surface of the inner core layer (or otheroptional intermediate core layers) in a dual-core ball are also readilydetermined according to the procedures given herein for measuring theouter surface hardness of a golf ball layer, if the measurement is madeprior to surrounding the layer with an additional core layer. Once anadditional core layer surrounds a layer of interest, the hardness of theinner and outer surfaces of any inner or intermediate layers can bedifficult to determine. Therefore, for purposes of the presentinvention, when the hardness of the inner or outer surface of a corelayer is needed after the inner layer has been surrounded with anothercore layer, the test procedure described above for measuring a pointlocated 1 mm from an interface is used. Likewise, the midpoint of a corelayer is taken at a point equidistant from the inner surface and outersurface of the layer to be measured, most typically an outer core layer.Also, once one or more core layers surround a layer of interest, theexact midpoint may be difficult to determine, therefore, for thepurposes of the present invention, the measurement of “midpoint”hardness of a layer is taken within ±1 mm of the measured midpoint ofthe layer.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and the hardness as measured directly on agolf ball. For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (i.e., a spherical surface)can result in a different hardness value. The difference in “surfacehardness” and “material hardness” values is due to several factorsincluding, but not limited to, ball construction (i.e., core type,number of cores and/or cover layers, and the like); ball diameter; andthe material composition of adjacent layers. It also should beunderstood that the two measurement techniques are not necessarilylinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore C or Shore Dhardness) was measured according to the test method ASTM D-2240.

The HNP compositions optionally comprise at least one additionalcopolymer component selected from partially neutralized ionomers andparticularly SURLYN® AD 1043, 1092, and 1022 ionomer resins,commercially available from DuPont; ionomers modified with rosins; softand resilient ethylene copolymers; polyolefins, such as linear,branched, or cyclic, C₂-C₄₀ olefins, particularly polymers comprisingethylene or propylene copolymerized with one or more C₂-C₄₀ olefins,C₃-C₂₀ α-olefins, or C₃-C₁₀ α-olefins; polyamides; polyesters;polyethers; polycarbonates; polysulfones; polyacetals; polylactones;acrylonitrile-butadiene-styrene resins; polyphenylene oxide;polyphenylene sulfide; styrene-acrylonitrile resins; styrene maleicanhydride; polyimides; aromatic polyketones; grafted and non-graftedmetallocene-catalyzed polymers, such as single-site catalyst polymerizedpolymers, high crystalline acid polymers, cationic ionomers, andcombinations thereof.

Other polymer components that may be included in the plasticized HNPcomposition include, for example, natural and synthetic rubbers,including, but not limited to, ethylene propylene rubber, ethylenepropylene diene rubber, styrenic block copolymer rubbers (such as SI,SIS, SB, SBS, SIBS, and the like, where “S” is styrene, “I” isisobutylene, and “B” is butadiene), SEBS, butyl rubber, halobutylrubber, copolymers of isobutylene and para-alkylstyrene, halogenatedcopolymers of isobutylene and para-alkylstyrene, natural rubber,polyisoprene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber (such as ethylene-alkyl acrylatesand ethylene-alkyl methacrylates, and, more specifically, ethylene-ethylacrylate, ethylene-methyl acrylate, and ethylene-butyl acrylate),chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber,and polybutadiene rubber.

The plasticized HNP compositions of the present invention, preferablyhave a specific gravity of about 0.90 g/cc to 1.00 g/cc, more preferablyabout 0.95 g/cc to 0.99 g/cc. Any suitable filler, flake, fiber,particle, or the like, of an organic or inorganic material may be addedto the HNP compositions to increase or decrease the specific gravity.

In a particular embodiment, the HNP compositions are formed by blendingan acid copolymer, a non-acid polymer, a cation source, and a fatty acidor metal salt thereof. The resulting HNP compositions are then combinedwith a plasticizer. For purposes of the present invention, maleicanhydride modified polymers are defined herein as a non-acid polymerdespite having anhydride groups that can ring-open to the acid formduring processing of the polymer to form the HNP compositions herein.The maleic anhydride groups are grafted onto a polymer, are present atrelatively very low levels, and are not part of the polymer backbone, asis the case with the acid polymers, which are exclusively E/X and E/X/Ycopolymers of ethylene and an acid, particularly methacrylic acid andacrylic acid. In a particular aspect of this embodiment, the acidcopolymer comprises ethylene-acrylic acid and ethylene-methacrylic acidcopolymers. The acid copolymer preferably has an acid content of about 2wt % to about 30 wt %, more preferably about 10 wt % to about 26 wt %,most preferably about 16 wt % to about 20 wt %. The present invention isnot meant to be limited by a particular order for combining and reactingthe acid polymer, non-acid polymer, and cation source. In a particularembodiment, the fatty acid or metal salt thereof is used in an amountsuch that the fatty acid or metal salt thereof is present in the HNPcomposition in an amount of about 10 wt % to 60 wt %, more preferablyabout 20 wt % to about 50 wt %, most preferably about 30 wt % to about40 wt %, based on the total weight of the HNP composition.

In another particular aspect of this embodiment, the acid copolymer isan ethylene-acrylic acid copolymer having an acid content of 19 wt % orgreater, the non-acid polymer is a metallocene-catalyzed ethylene-butenecopolymer, optionally modified with maleic anhydride, the cation sourceis magnesium, and the fatty acid or metal salt thereof is magnesiumoleate present in the composition in an amount of 20 to 50 wt %, basedon the total weight of the composition. This preferred HNP compositionis treated with a plasticizer as described below.

The ethylene acid copolymer may be blended with other materialsincluding, but not limited to, partially- and fully-neutralized ionomersoptionally blended with a maleic anhydride-grafted non-ionomericpolymer, graft copolymers of ionomer and polyamide, and the followingnon-ionomeric polymers, including homopolymers and copolymers thereof,as well as their derivatives that are compatibilized with at least onegrafted or copolymerized functional group, such as maleic anhydride,amine, epoxy, isocyanate, hydroxyl, sulfonate, phosphonate, and thelike.

In a particular embodiment, the plasticized thermoplastic compositioncomprises a fully-neutralized ionomer optionally blended with a maleicanhydride-grafted non-ionomeric polymer, polyesters, polyamides,polyethers, and blends of two or more thereof and plasticizer.

The plasticized thermoplastic composition may be treated or admixed witha thermoset diene composition to reduce or prevent flow uponovermolding. Optional treatments may also include the addition ofperoxide to the material prior to molding, or a post-molding treatmentwith, for example, a crosslinking solution, electron beam, gammaradiation, isocyanate or amine solution treatment, or the like. Suchtreatments may prevent the intermediate layer from melting and flowingor “leaking” out at the mold equator, as the thermoset outer core layeris molded thereon at a temperature necessary to crosslink the outer corelayer, which is typically from 280° F. to 360° F. for a period of about5 to 30 min.

The plasticized HNP compositions of the present invention, optionally,include additives and/or fillers in an amount of about 5 wt % to about50 wt %, more preferably about 10 wt % to about 30 wt %, and mostpreferably about 15 wt % to about 25 wt %, based on the total weight ofthe composition. Suitable additives and fillers include, but are notlimited to, chemical blowing and foaming agents, optical brighteners,coloring agents, fluorescent agents, whitening agents, UV absorbers,light stabilizers, defoaming agents, processing aids, mica, talc,nano-fillers, antioxidants, stabilizers, softening agents, fragrancecomponents, impact modifiers, TiO₂, acid copolymer wax, surfactants, andfillers, such as zinc oxide, tin oxide, barium sulfate, zinc sulfate,calcium oxide, calcium carbonate, zinc carbonate, barium carbonate,clay, tungsten, tungsten carbide, silica, lead silicate, regrind(recycled material), and mixtures thereof.

In one preferred embodiment, the core and/or core layers of theinvention are formed from a thermoplastic, plasticized composition thatincludes an acid copolymer of ethylene and an α,β-unsaturated carboxylicacid; an optional softening monomer, such as alkyl acrylate or alkylmethacrylate; a plasticizer; and a cation source present in an amountsufficient to neutralize about 0% to 100% of all acid groups present inthe plasticized composition. Additionally, an optional organic acid orsat thereof may also be present to effect some or all of theneutralization.

The cores (and, preferably the inner core layer) may also be formed from(or contain as part of a blend) thermoplastic non-ionomer resins. Thesepolymers typically have a hardness in the range of 20 Shore D to 70Shore D. Examples of thermoplastic non-ionomers include, but are notlimited to, ethylene-ethyl acrylate, ethylene-methyl acrylate,ethylene-vinyl acetate, low density polyethylene, linear low densitypolyethylene, metallocene catalyzed polyolefins, polyamides includingnylon copolymers and nylon-ionomer graft copolymers, non-ionomeric acidcopolymers, and a variety of thermoplastic elastomers, includingstyrene-butadiene-styrene block copolymers, thermoplastic blockpolyamides, polyurethanes, polyureas, thermoplastic block polyesters,functionalized (e.g., maleic anhydride modified) EPR and EPDM, andsyndiotactic butadiene resin.

In order to obtain the desired Shore D hardness, it may be necessary toadd one or more crosslinking monomers and/or reinforcing agents to thepolymer composition. Nonlimiting examples of crosslinking monomers arezinc diacrylate, zinc dimethacrylate, ethylene dimethacrylate,trimethylol propane triacrylate. If crosslinking monomers are used, theytypically are added in an amount of 3 to 40 parts (by weight based upon100 parts by weight of polymer), and more preferably 5 to 30 parts.

Other layers of a dual core, preferably the outer core layer, may beformed from a rubber-based composition treated to define a shallow“positive” hardness gradient, and preferably the inner core layer isformed from the thermoplastic material of the invention and has a“positive” or preferably “negative” hardness gradient. For example, theinner core may be formed from the ‘hardness gradient’ thermoplasticmaterial of the invention and the outer core layer may include therubber composition (or vice versa). A base thermoset rubber, which canbe blended with other rubbers and polymers, typically includes a naturalor synthetic rubber. A preferred base rubber is 1,4-polybutadiene havinga cis structure of at least 40%, preferably greater than 80%, and morepreferably greater than 90%. Other suitable thermoset rubbers andpreferred properties, such as Mooney viscosity, are disclosed in U.S.Pat. No. 7,351,165, filed Mar. 13, 2007, and U.S. Pat. No. 7,458,905,filed Mar. 23, 2007, both of which are incorporated herein by reference.

Other thermoplastic elastomers may be used to modify the properties ofthe thermoplastic materials of the invention by blending with the basethermoplastic material. These TPEs include natural or synthetic balata,or high trans-polyisoprene, high trans-polybutadiene, or any styrenicblock copolymer, such as styrene ethylene butadiene styrene,styrene-isoprene-styrene, etc., a metallocene or other single-sitecatalyzed polyolefin such as ethylene-octene, or ethylene-butene, orthermoplastic polyurethanes (TPU), including copolymers, e.g. withsilicone. Other suitable TPEs include PEBAX®, which is believed tocomprise polyether amide copolymers, HYTREL®, which is believed tocomprise polyether ester copolymers, thermoplastic urethane, andKRATON®, which is believed to comprise styrenic block copolymerselastomers. Any of the TPEs or TPUs above may also contain functionalitysuitable for grafting, including maleic acid or maleic anhydride.

Additional polymers may also optionally be incorporated into theinventive cores. Examples include, but are not limited to, thermosetelastomers such as core regrind, thermoplastic vulcanizate, copolymericionomer, terpolymeric ionomer, polycarbonate, polyamide, copolymericpolyamide, polyesters, polyvinyl alcohols,acrylonitrile-butadiene-styrene copolymers, polyarylate, polyacrylate,polyphenylene ether, impact-modified polyphenylene ether, high impactpolystyrene, diallyl phthalate polymer, styrene-acrylonitrile polymer(SAN) (including olefin-modified SAN andacrylonitrile-styrene-acrylonitrile polymer), styrene-maleic anhydridecopolymer, styrenic copolymer, functionalized styrenic copolymer,functionalized styrenic terpolymer, styrenic terpolymer, cellulosepolymer, liquid crystal polymer, ethylene-vinyl acetate copolymers,polyurea, and polysiloxane or any metallocene-catalyzed polymers ofthese species.

Suitable polyamides for use as an additional polymeric material incompositions within the scope of the present invention also includeresins obtained by: (1) polycondensation of (a) a dicarboxylic acid,such as oxalic acid, adipic acid, sebacic acid, terephthalic acid,isophthalic acid, or 1,4-cyclohexanedicarboxylic acid, with (b) adiamine, such as ethylenediamine, tetramethylenediamine,pentamethylenediamine, hexamethylenediamine, or decamethylenediamine,1,4-cyclohexanediamine, or m-xylylenediamine; (2) a ring-openingpolymerization of cyclic lactam, such as ε-caprolactam or Ω-laurolactam;(3) polycondensation of an aminocarboxylic acid, such as 6-aminocaproicacid, 9-aminononanoic acid, 11-aminoundecanoic acid, or12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam witha dicarboxylic acid and a diamine. Specific examples of suitablepolyamides include NYLON 6, NYLON 66, NYLON 610, NYLON 11, NYLON 12,copolymerized NYLON, NYLON MXD6 (m-xylylene diamine/adipic acid), andNYLON 46.

Modifications in thermoplastic polymeric structure to create thehardness gradient can be induced by a number of methods, includingexposing the TP material to high-energy radiation or through a chemicalprocess using peroxide. Radiative sources include, but are not limitedto, gamma rays, electrons, neutrons, protons, x-rays, helium nuclei, orthe like. Gamma radiation, typically using radioactive cobalt atoms, isa preferred method for the inventive TP gradient cores because this typeof radiation allows for considerable depth of treatment, if necessary.For cores requiring lower depth of penetration, such as when a smallgradient is desired, electron-beam accelerators or UV and IR lightsources can be used. Useful UV and IR irradiation methods are disclosedin U.S. Pat. Nos. 6,855,070 and 7,198,576, which are incorporated hereinby reference thereto. The cores of the invention are typicallyirradiated at dosages greater than 0.05 Mrd, preferably ranging from 1Mrd to 20 Mrd, more preferably from 2 Mrd to 15 Mrd, and most preferablyfrom 4 Mrd to 10 Mrd. In one preferred embodiment, the cores areirradiated at a dosage from 5 Mrd to 8 Mrd and in another preferredembodiment, the cores are irradiated with a dosage from 0.05 Mrd to 3Mrd, more preferably 0.05 Mrd to 1.5 Mrd. In these preferredembodiments, is also desirable to irradiate the cores for a longer timedue to the low dosage and in an effort to create a larger TP hardnessgradient, either positive or negative, preferably negative.

While a number of methods known in the art are suitable for irradiatingthe TP (or TS) materials/cores, typically the cores are placed on andslowly move along a channel. Radiation from a radiation source, such asgamma rays, is allowed to contact the surface of the cores. The sourceis positioned to provide a generally uniform dose of radiation to thecores as they roll along the channel. The speed of the cores as theypass through the radiation source is easily controlled to ensure thecores receive sufficient dosage to create the desired hardness gradient.The cores are irradiated with a dosage of 1 or more Mrd, more preferably2 Mrd to 15 Mrd. The intensity of the dosage is typically in the rangeof 1 MeV to 20 MeV.

For thermoplastic resins having a reactive group (e.g., ionomer,thermoplastic urethane, etc.), treating the thermoplastic core in achemical solution of an isocyanate or and amine affects crosslinking andprovide a harder surface and subsequent hardness gradient. Incorporationof peroxide or other free-radical initiator in the thermoplasticpolymer, prior to molding or forming, also allows for heat curing on themolded core/core layer to create the desired gradient. By properselection of time/temperature, an annealing process can be used tocreate a gradient. Suitable annealing and/or peroxide (free radical)methods are such as disclosed in U.S. Pat. Nos. 5,274,041 and 5,356,941,respectively, which are incorporated by reference thereto. Additionally,silane or amino-silane crosslinking may also be employed as disclosed inU.S. Pat. No. 7,279,529, filed Jun. 7, 2004, and incorporated herein byreference.

The inventive cores (or core layers) may be chemically treated in asolution, such as a solution containing one or more isocyanates, to formthe desired hardness gradient. The cores are typically exposed to thesolution containing the isocyanate by immersing them in a bath at aparticular temperature for a given time. Exposure time should be greaterthan 1 minute, preferably from 1 minute to 120 minutes, more preferably5 minutes to 90 minutes, and most preferably 10 minutes to 60 minutes.In one preferred embodiment, the cores are immersed in the treatingsolution from 15 minutes to 45 minutes, more preferably from 20 minutesto 40 minutes, and most preferably from 25 minutes to 30 minutes.

Preferred isocyanates include aliphatic or aromatic isocyanates, such asHDI, IPDI, MDI, TDI, or diisocyanate or blends thereof known in the art.The isocyanate or diisocyanate used may have a solids content in therange of 1 wt % to 100 wt % solids, preferably 5 wt % to 50 wt % solids,most preferably 10 wt % to 30 wt % solids. In a most preferredembodiment, the cores of the invention are immersed in a solution of MDI(such as Mondur ML™, commercially available from Bayer) at 15 wt % to 30wt % solids in ketone for 20 minutes to 30 minutes. Suitable solvents(i.e., those that will allow penetration of the isocyanate into the TPmaterial) may be used. Preferred solvents include ketone and acetate.After immersion, the balls are typically air-dried and/or heated.Suitable isocyanates and treatment methods are disclosed in U.S. Pat.No. 7,118,496, which is incorporated herein by reference thereto.

Preferred silanes include, but are not limited to, compounds having theformula:

wherein R′ is a non-hydrolysable organofunctional group, X is ahydrolysable group, and n is 0-24. The non-hydrolysable organofunctionalgroup typically can link (either by forming a covalent or by anotherbinding mechanism, such as hydrogen bond) to a polymer, such as apolyolefin, thereby attaching the silane to the polymer. R′ ispreferably a vinyl group. X is preferably alkoxy, acyloxy, halogen,amino, hydrogen, ketoximate group, amido group, aminooxy, mercapto,alkenyloxy group, and the like. Preferably, X is an alkoxy, RO—, whereinR is selected from the group consisting of a linear or branched C₁-C₈alkyl group, a C₆-C₁₂ aromatic group, and R³C(O)—, wherein R³ is alinear or branched C₁-C₈ alkyl group. Typically, the silane can belinked to the polymer in one of two ways: by reaction of the silane tothe finished polymer or copolymerizing the silane with the polymerprecursors.

A preferred silane may also have the formula R′—(CH₂)_(n)SiX_(k)Q_(m) or[R′—(CH₂)_(n)]₂Si(X)_(p)Q_(q), wherein R′ is an unsaturated vinyl group;Q is selected from the group consisting of an isocyanate functionality,i.e., a monomer, a biuret, or an isocyanurate; a glycidyl, a halo groupand —NR¹R², wherein R¹ and R² are each independently selected from thegroup consisting of H, a linear or branched C₁-C₈ alkyl group, a linearor branched C₁-C₈ alkenyl group and a linear or branched C₁-C₈ alkynylgroup; X is a hydrolysable group; and n is 0-24, k is 1-3, m is 3-n, pis 1-2 and q is 2-p. X is preferably alkoxy, acyloxy, halogen, amino,hydrogen, ketoximate group, amido group, aminooxy, mercapto, alkenyloxygroup, and the like. Preferably, the halo group is fluoro, chloro, bromoor iodo and is preferably chloro.

The unsaturated group A is represented by the formula:

wherein R¹, R², and R³ are each independently selected from the groupconsisting of a substituted or unsubstituted linear or branched C₁-C₈alkyl group, a substituted or unsubstituted C₆-C₁₂ aromatic group and ahalo group. Preferred halo groups include F, Cl or Br. The C₁-C₈ alkylgroups and the C₆-C₁₂ aromatic groups may be substituted with one ormore C₁-C₆ alkyl groups, halo groups, such as F, Cl and Br, amines, CN,C₁-C₆ alkoxy groups, trihalomethane, such as CF₃ or CCl₃, or mixturesthereof. Preferably, R¹, R², and R³ are each independently selected fromthe group consisting of hydrogen, methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl and tert-butyl. More preferably, R¹, R², and R³ areeach independently hydrogen or methyl.

Thus in a preferred embodiment, the silane is a vinyltrialkoxysilane,such as vinyltrimethoxysilane, vinyldimethoxysilane,vinyltrimethoxysilane, vinylmethoxysilane, vinyltriethoxysilane,vinyldiphenylchlorosilane, vinyltrichlorosilane, vinylsilane,(vinyl)(methyl)diethoxysilane, vinyltriacetoxysilane,vinyltris(2-methoxyethoxy)silane, vinyl triphenylsilane, and(vinyl)(dimethyl)chlorosilane.

The silanes of the present invention are present from about 0.1 weightpercent to about 100 weight percent of the polyolefin. Typically, thesilanes are present from about 0.5 weight percent to about 50 weightpercent of the polyolefin, preferably from about 1 weight percent toabout 20 weight percent of the polyolefin, more preferably from about 2weight percent to about 10 weight percent of polyolefin and even morepreferably from about 3 weight percent to about 5 weight percent. Asused herein, all upper and lower limits of the ranges disclosed hereincan be interchanged to form new ranges. Thus, the present invention alsoencompasses silane amounts of from about 0.1 weight percent to about 5weight percent of polyolefin, from about 1 weight percent to about 10weight percent of polyolefin, and even from 20 weight percent to about50 weight percent.

Commercially available silanes for moisture crosslinking may be used toform golf ball components and golf balls. A nonlimiting example of asuitable silane is SILCAT® RHS Silane, a multi-component crosslinkingsystem for use in moisture crosslinking of stabilized polyethylene orethylene copolymers (available at Crompton Corporation, Middlebury,Conn.). IN addition, functionalized resin systems also may be used, suchas SYNCURE®, which is a silane-grafted, moisture-crosslinkablepolyethylene system available from PolyOne Corporation of Cleveland,Ohio, POLIDAN®, which is a silane-crosslinkable HDPE available fromSolvay of Padanaplast, Italy, and VISICO™/AMBICAT™, which is apolyethylene system that utilizes a non-tin catalyst in crosslinkingavailable from Borealis of Denmark.

Other suitable silanes include, but are not limited to, silane esters,such as octyltriethoxysilane, methyltriethoxylsilane,methyltrimethoxysilane, and proprietary nonionic silane dispersingagent; vinyl silanes, such as proprietary, vinyltriethoxysilane,vinyltrimethoxysilane, vinyl-tris-(2-methoxyethoxy) silane,vinylmethyldimethoxysilane; methacryloxy silanes, such asγ-methacryloxypropyltrimethoxysilane; epoxy silanes, such asβ-(3,4-epoxycyclohexyl) ethyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane; sulfur silanes, such asgamma-mercaptopropyltrimethoxysilane proprietary polysulfidesilane,bis-(3-[triethoxisily](-propyl)-tetrasulfane; amino silanes, such asγ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane,γ-aminopropyltriethoxysilane, aminoalkyl silicone solution, modifiedaminoorganosilane, gamma-aminopropyltrimethoxysilane,n-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, modifiedaminoorganosilane (40% in methanol), modified aminosilane (50% inmethanol), triaminofunctional silane,bis-(γ-trimethoxysilylpropyl)amine,n-phenyl-γ-aminopropyltrimethoxysilane, organomodifiedpolydimethylsiloxane, polyazamide silane (50% in methanol),n-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane; ureido silanes,such as gamma-ureidopropyltrialkoxysilane (50% in methanol),γ-ureidopropyltrimethoxysilane; isocyanate silanes, such asγ-isocyanatopropyltriethoxysilane; and mixtures thereof. Preferably, thesilane is an amino silane and more preferably, the amino silane isbis-(γ-trimethoxysilylpropyl)amine.

Both irradiative and chemical methods promote molecular bonding, orcross-links, within the TP polymer. Radiative methods permitcross-linking and grafting in situ on finished products andcross-linking occurs at lower temperatures with radiation than withchemical processing. Chemical methods depend on the particular polymer,the presence of modifying agents, and variables in processing, such asthe level of irradiation. Significant property benefits in the TP corescan be attained and include, but are not limited to, improvedthermomechanical properties; lower permeability and improved chemicalresistance; reduced stress cracking; and overall improvement in physicaltoughness.

Additional embodiments involve the use of plasticizers to treat themolded core/layer thereby creating a softer outer portion of the corefor a “negative” hardness gradient. The plasticizer may be reactive(such as higher alkyl acrylates) or non-reactive (i.e., phthalates,dioctylphthalate, or stearamides, etc). Other suitable plasticizersinclude, but are not limited to, oxa acids, fatty amines, fatty amides,fatty acid esters, phthalates, adipates, and sebacates. Oxa acids arepreferred plasticizers, more preferably those having at least one or twoacid functional groups and a variety of different chain lengths.Preferred oxa acids include 3,6-dioxaheptanoic acid,3,6,9-trioxadecanoic acid, diglycolic acid, 3,6,9-trioxaundecanoic acid,polyglycol diacid, and 3,6-dioxaoctanedioic acid, such as thosecommercially available from Archimica of Wilmington, Del. Oleic acidesters are particularly preferred and include, but are not limited to,methyl oleate, ethyl oleate, butyl oleate, 2-ethylhexyl oleate, and soforth.

Any means of chemical degradation will also give the desired “negative”hardness gradient. Chemical modifications such as esterification orsaponification are also suitable for modification of the thermoplasticcore/layer surface.

Fillers may also be added to the thermoplastic materials of the core toadjust the density of the material up or down.

The shallow “positive” hardness gradient outer core layer(s) are formedfrom a composition including at least one thermoset base rubber, such asa polybutadiene rubber, cured with at least one peroxide and at leastone reactive co-agent, which can be a metal salt of an unsaturatedcarboxylic acid, such as acrylic acid or methacrylic acid, anon-metallic coagent, or mixtures thereof. Preferably, for the“negative” hardness gradient core embodiment, a suitable antioxidant isincluded in the composition. An optional soft and fast agent (andsometimes a cis-to-trans catalyst), such as an organosulfur ormetal-containing organosulfur compound, can also be included in the coreformulation.

Other ingredients that are known to those skilled in the art may beused, and are understood to include, but not be limited to,density-adjusting fillers, process aides, plasticizers, blowing orfoaming agents, sulfur accelerators, and/or non-peroxide radicalsources.

The base thermoset rubber, which can be blended with other rubbers andpolymers, typically includes a natural or synthetic rubber. A preferredbase rubber is 1,4-polybutadiene having a cis structure of at least 40%,preferably greater than 80%, and more preferably greater than 90%.

Examples of desirable polybutadiene rubbers include and TAKTENE® 1203G1,220, 221, BUNA® CB22 and BUNA® CB23, commercially available from LANXESSCorporation; UBEPOL® 360L and UBEPOL® 150L and UBEPOL-BR rubbers,commercially available from UBE Industries, Ltd. of Tokyo, Japan; KINEX®7245 and KINEX® 7265, commercially available from Goodyear of Akron,Ohio; SE BR-1220, commercially available from Dow Chemical Company;Europrene® NEOCIS® BR 40 and BR 60, commercially available from PolimeriEuropa; and BR 01, BR 730, BR 735, BR 11, and BR 51, commerciallyavailable from Japan Synthetic Rubber Co., Ltd; COPERFLEX® BRNd-40 fromPetroflex of Brazil; and KARBOCHEM® ND40, ND45, and ND60, commerciallyavailable from Karbochem.

The base rubber may also comprise high or medium Mooney viscosityrubber, or blends thereof. The measurement of Mooney viscosity isdefined according to ASTM D-1646. The Mooney viscosity range ispreferably greater than about 40, more preferably in the range fromabout 40 to about 80 and more preferably in the range from about 40 toabout 60. Polybutadiene rubber with higher Mooney viscosity may also beused, so long as the viscosity of the polybutadiene does not reach alevel where the high viscosity polybutadiene clogs or otherwiseadversely interferes with the manufacturing machinery. It iscontemplated that polybutadiene with viscosity less than 65 Mooney canbe used with the present invention. In one embodiment of the presentinvention, golf ball core layers made with mid- to high-Mooney viscositypolybutadiene material exhibit increased resiliency (and, therefore,distance) without increasing the hardness of the ball.

Commercial sources of suitable mid- to high-Mooney viscositypolybutadiene include Bayer AG CB23 (Nd-catalyzed), which has a Mooneyviscosity of around 50 and is a highly linear polybutadiene, and Dow1220 (Co-catalyzed). If desired, the polybutadiene can also be mixedwith other elastomers known in the art, such as other polybutadienerubbers, natural rubber, styrene butadiene rubber, and/or isoprenerubber in order to further modify the properties of the core. When amixture of elastomers is used, the amounts of other constituents in thecore composition are typically based on 100 parts by weight of the totalelastomer mixture.

In one preferred embodiment, the base rubber comprises a Nd-catalyzedpolybutadiene, a rare earth-catalyzed polybutadiene rubber, or blendsthereof. If desired, the polybutadiene can also be mixed with otherelastomers known in the art such as natural rubber, polyisoprene rubberand/or styrene-butadiene rubber in order to modify the properties of thecore. Other suitable base rubbers include thermosetting materials suchas, ethylene propylene diene monomer rubber, ethylene propylene rubber,butyl rubber, halobutyl rubber, hydrogenated nitrile butadiene rubber,nitrile rubber, and silicone rubber.

Thermoplastic elastomers (TPE) many also be used to modify theproperties of the core layers, or the uncured core layer stock byblending with the base thermoset rubber. These TPEs include natural orsynthetic balata, or high trans-polyisoprene, high trans-polybutadiene,or any styrenic block copolymer, such as styrene ethylene butadienestyrene, styrene-isoprene-styrene, etc., a metallocene or othersingle-site catalyzed polyolefin such as ethylene-octene, orethylene-butene, or thermoplastic polyurethanes (TPU), includingcopolymers, e.g. with silicone. Other suitable TPEs for blending withthe thermoset rubbers of the present invention include PEBAX®, which isbelieved to comprise polyether amide copolymers, HYTREL®, which isbelieved to comprise polyether ester copolymers, thermoplastic urethane,and KRATON®, which is believed to comprise styrenic block copolymerselastomers. Any of the TPEs or TPUs above may also contain functionalitysuitable for grafting, including maleic acid or maleic anhydride.

Additional polymers may also optionally be incorporated into the baserubber. Examples include, but are not limited to, thermoset elastomerssuch as core regrind, thermoplastic vulcanizate, copolymeric ionomer,terpolymeric ionomer, polycarbonate, polyamide, copolymeric polyamide,polyesters, polyvinyl alcohols, acrylonitrile-butadiene-styrenecopolymers, polyarylate, polyacrylate, polyphenylene ether,impact-modified polyphenylene ether, high impact polystyrene, diallylphthalate polymer, styrene-acrylonitrile polymer (SAN) (includingolefin-modified SAN and acrylonitrile-styrene-acrylonitrile polymer),styrene-maleic anhydride copolymer, styrenic copolymer, functionalizedstyrenic copolymer, functionalized styrenic terpolymer, styrenicterpolymer, cellulose polymer, liquid crystal polymer, ethylene-vinylacetate copolymers, polyurea, and polysiloxane or anymetallocene-catalyzed polymers of these species.

Suitable polyamides for use as an additional polymeric material incompositions within the scope of the present invention also includeresins obtained by: (1) polycondensation of (a) a dicarboxylic acid,such as oxalic acid, adipic acid, sebacic acid, terephthalic acid,isophthalic acid, or 1,4-cyclohexanedicarboxylic acid, with (b) adiamine, such as ethylenediamine, tetramethylenediamine,pentamethylenediamine, hexamethylenediamine, or decamethylenediamine,1,4-cyclohexanediamine, or m-xylylenediamine; (2) a ring-openingpolymerization of cyclic lactam, such as ε-caprolactam or Ω-laurolactam;(3) polycondensation of an aminocarboxylic acid, such as 6-aminocaproicacid, 9-aminononanoic acid, 11-aminoundecanoic acid, or12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam witha dicarboxylic acid and a diamine. Specific examples of suitablepolyamides include NYLON 6, NYLON 66, NYLON 610, NYLON 11, NYLON 12,copolymerized NYLON, NYLON MXD6, and NYLON 46.

Suitable peroxide initiating agents include dicumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy) hexane;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne;2,5-dimethyl-2,5-di(benzoylperoxy)hexane;2,2′-bis(t-butylperoxy)-di-iso-propylbenzene;1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane; n-butyl4,4-bis(t-butyl-peroxy)valerate; t-butyl perbenzoate; benzoyl peroxide;n-butyl 4,4′-bis(butylperoxy) valerate; di-t-butyl peroxide; or2,5-di-(t-butylperoxy)-2,5-dimethyl hexane, lauryl peroxide, t-butylhydroperoxide, α-α bis(t-butylperoxy) diisopropylbenzene,di(2-t-butyl-peroxyisopropyl)benzene, di-t-amyl peroxide, di-t-butylperoxide. Preferably, the rubber composition includes from about 0.25 toabout 5.0 parts by weight peroxide per 100 parts by weight rubber (phr),more preferably 0.5 phr to 3 phr, most preferably 0.5 phr to 1.5 phr. Ina most preferred embodiment, the peroxide is present in an amount ofabout 0.8 phr. These ranges of peroxide are given assuming the peroxideis 100% active, without accounting for any carrier that might bepresent. Because many commercially available peroxides are sold alongwith a carrier compound, the actual amount of active peroxide presentmust be calculated. Commercially-available peroxide initiating agentsinclude DICUP™ family of dicumyl peroxides (including DICUP™ R, DICUP™40C and DICUP™ 40KE) available from Crompton (Geo Specialty Chemicals).Similar initiating agents are available from AkroChem, Lanxess,Flexsys/Harwick and R.T. Vanderbilt. Another commercially-available andpreferred initiating agent is TRIGONOX™ 265-50B from Akzo Nobel, whichis a mixture of 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane anddi(2-t-butylperoxyisopropyl) benzene. TRIGONOX™ peroxides are generallysold on a carrier compound.

Suitable reactive co-agents include, but are not limited to, metal saltsof diacrylates, dimethacrylates, and monomethacrylates suitable for usein this invention include those wherein the metal is zinc, magnesium,calcium, barium, tin, aluminum, lithium, sodium, potassium, iron,zirconium, and bismuth. Zinc diacrylate (ZDA) is preferred, but thepresent invention is not limited thereto. ZDA provides golf balls with ahigh initial velocity. The ZDA can be of various grades of purity. Forthe purposes of this invention, the lower the quantity of zinc stearatepresent in the ZDA the higher the ZDA purity. ZDA containing less thanabout 10% zinc stearate is preferable. More preferable is ZDA containingabout 4-8% zinc stearate. Suitable, commercially available zincdiacrylates include those from Sartomer Co. The preferred concentrationsof ZDA that can be used are about 10 phr to about 55 phr, preferably 10phr to about 40 phr, alternatively about 15 phr to about 40 phr, morepreferably 20 phr to about 35 phr, most preferably 25 phr to about 35phr. In a particularly preferred embodiment, the reactive co-agent ispresent in an amount of about 21 phr to 31 phr, preferably about 29 phrto about 31 phr.

Additional preferred co-agents that may be used alone or in combinationwith those mentioned above include, but are not limited to,trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, andthe like. It is understood by those skilled in the art, that in the casewhere these co-agents may be liquids at room temperature, it may beadvantageous to disperse these compounds on a suitable carrier topromote ease of incorporation in the rubber mixture.

Antioxidants are compounds that inhibit or prevent the oxidativebreakdown of elastomers, and/or inhibit or prevent reactions that arepromoted by oxygen radicals. Some exemplary antioxidants that may beused in the present invention include, but are not limited to, quinolinetype antioxidants, amine type antioxidants, and phenolic typeantioxidants. A preferred antioxidant is2,2′-methylene-bis-(4-methyl-6-t-butylphenol) available as VANOX® MBPCfrom R.T. Vanderbilt. Other polyphenolic antioxidants include VANOX® T,VANOX® L, VANOX® SKT, VANOX® SWP, VANOX® 13 and VANOX® 1290.

Preferably, about 0.25 phr to about 1.5 phr of peroxide as calculated at100% active can be added to the core formulation, more preferably about0.5 phr to about 1.2 phr, and most preferably about 0.7 phr to about 1.0phr. The ZDA amount can be varied to suit the desired compression, spinand feel of the resulting golf ball. The cure regime can have atemperature range between from about 290° F. to about 335° F., morepreferably about 300° F. to about 325° F., and the stock is held at thattemperature for at least about 10 minutes to about 30 minutes.

If a steep “positive” hardness gradient is desired across any rubberlayer, a gradient-promoting additive (GPA) should be present. SuitableGPA's include, but are not limited to benzoquinones, resorcinols,catechols, quinhydrones, and hydroquinones. Those, and other methods andmaterial for creating a steep “positive” hardness gradient are disclosedin U.S. patent application Ser. Nos. 12/168,979; 12/168,987; 12/168,995;and Ser. No. 12/169,002, which are incorporated herein by referencethereto.

The thermoset rubber composition of the present invention may alsoinclude an optional soft and fast agent. As used herein, “soft and fastagent” means any compound or a blend thereof that that is capable ofmaking a core 1) be softer (lower compression) at constant COR or 2)have a higher COR at equal compression, or any combination thereof, whencompared to a core equivalently prepared without a soft and fast agent.Preferably, the composition of the present invention contains from about0.05 phr to about 10.0 phr soft and fast agent. In one embodiment, thesoft and fast agent is present in an amount of about 0.05 phr to about3.0 phr, preferably about 0.05 phr to about 2.0 phr, more preferablyabout 0.05 phr to about 1.0 phr. In another embodiment, the soft andfast agent is present in an amount of about 2.0 phr to about 5.0 phr,preferably about 2.35 phr to about 4.0 phr, and more preferably about2.35 phr to about 3.0 phr. In an alternative high concentrationembodiment, the soft and fast agent is present in an amount of about 5.0phr to about 10.0 phr, more preferably about 6.0 phr to about 9.0 phr,most preferably about 7.0 phr to about 8.0 phr. In a most preferredembodiment, the soft and fast agent is present in an amount of about 2.6phr.

Suitable soft and fast agents include, but are not limited to,organosulfur or metal-containing organosulfur compounds, an organicsulfur compound, including mono, di, and polysulfides, a thiol, ormercapto compound, an inorganic sulfide compound, a Group VIA compound,or mixtures thereof. The soft and fast agent component may also be ablend of an organosulfur compound and an inorganic sulfide compound.

Suitable soft and fast agents of the present invention include, but arenot limited to those having the following general formula:

where R₁-R₅ can be C₁-C₈ alkyl groups; halogen groups; thiol groups(—SH), carboxylated groups; sulfonated groups; and hydrogen; in anyorder; and also pentafluorothiophenol; 2-fluorothiophenol;3-fluorothiophenol; 4-fluorothiophenol; 2,3-fluorothiophenol;2,4-fluorothiophenol; 3,4-fluorothiophenol; 3,5-fluorothiophenol2,3,4-fluorothiophenol; 3,4,5-fluorothiophenol;2,3,4,5-tetrafluorothiophenol; 2,3,5,6-tetrafluorothiophenol;4-chlorotetrafluorothiophenol; pentachlorothiophenol;2-chlorothiophenol; 3-chlorothiophenol; 4-chlorothiophenol;2,3-chlorothiophenol; 2,4-chlorothiophenol; 3,4-chlorothiophenol;3,5-chlorothiophenol; 2,3,4-chlorothiophenol; 3,4,5-chlorothiophenol;2,3,4,5-tetrachlorothiophenol; 2,3,5,6-tetrachlorothiophenol;pentabromothiophenol; 2-bromothiophenol; 3-bromothiophenol;4-bromothiophenol; 2,3-bromothiophenol; 2,4-bromothiophenol;3,4-bromothiophenol; 3,5-bromothiophenol; 2,3,4-bromothiophenol;3,4,5-bromothiophenol; 2,3,4,5-tetrabromothiophenol;2,3,5,6-tetrabromothiophenol; pentaiodothiophenol; 2-iodothiophenol;3-iodothiophenol; 4-iodothiophenol; 2,3-iodothiophenol;2,4-iodothiophenol; 3,4-iodothiophenol; 3,5-iodothiophenol;2,3,4-iodothiophenol; 3,4,5-iodothiophenol; 2,3,4,5-tetraiodothiophenol;2,3,5,6-tetraiodothiophenoland; and their zinc salts. Preferably, thehalogenated thiophenol compound is pentachlorothiophenol, which iscommercially available in neat form or under the tradename STRUKTOL®, aclay-based carrier containing the sulfur compound pentachlorothiophenolloaded at 45 percent (correlating to 2.4 parts PCTP). STRUKTOL® iscommercially available from Struktol Company of America of Stow, Ohio.PCTP is commercially available in neat form from eChinachem of SanFrancisco, Calif. and in the salt form from eChinachem of San Francisco,Calif. Most preferably, the halogenated thiophenol compound is the zincsalt of pentachlorothiophenol, which is commercially available fromeChinachem of San Francisco, Calif.

As used herein when referring to the invention, the term “organosulfurcompound(s)” refers to any compound containing carbon, hydrogen, andsulfur, where the sulfur is directly bonded to at least 1 carbon. Asused herein, the term “sulfur compound” means a compound that iselemental sulfur, polymeric sulfur, or a combination thereof. It shouldbe further understood that the term “elemental sulfur” refers to thering structure of S₈ and that “polymeric sulfur” is a structureincluding at least one additional sulfur relative to elemental sulfur.

Additional suitable examples of soft and fast agents (that are alsobelieved to be cis-to-trans catalysts) include, but are not limited to,4,4′-diphenyl disulfide; 4,4′-ditolyl disulfide; 2,2′-benzamido diphenyldisulfide; bis(2-aminophenyl) disulfide; bis(4-aminophenyl) disulfide;bis(3-aminophenyl) disulfide; 2,2′-bis(4-aminonaphthyl) disulfide;2,2′-bis(3-aminonaphthyl) disulfide; 2,2′-bis(4-aminonaphthyl)disulfide; 2,2′-bis(5-aminonaphthyl) disulfide;2,2′-bis(6-aminonaphthyl) disulfide; 2,2′-bis(7-aminonaphthyl)disulfide; 2,2′-bis(8-aminonaphthyl) disulfide;1,1′-bis(2-aminonaphthyl) disulfide; 1,1′-bis(3-aminonaphthyl)disulfide; 1,1′-bis(3-aminonaphthyl) disulfide;1,1′-bis(4-aminonaphthyl) disulfide; 1,1′-bis(5-aminonaphthyl)disulfide; 1,1′-bis(6-aminonaphthyl) disulfide;1,1′-bis(7-aminonaphthyl) disulfide; 1,1′-bis(8-aminonaphthyl)disulfide; 1,2′-diamino-1,2′-dithiodinaphthalene;2,3′-diamino-1,2′-dithiodinaphthalene; bis(4-chlorophenyl) disulfide;bis(2-chlorophenyl) disulfide; bis(3-chlorophenyl) disulfide;bis(4-bromophenyl) disulfide; bis(2-bromophenyl) disulfide;bis(3-bromophenyl) disulfide; bis(4-fluorophenyl) disulfide;bis(4-iodophenyl) disulfide; bis(2,5-dichlorophenyl) disulfide;bis(3,5-dichlorophenyl) disulfide; bis(2,4-dichlorophenyl) disulfide;bis(2,6-dichlorophenyl) disulfide; bis(2,5-dibromophenyl) disulfide;bis(3,5-dibromophenyl) disulfide; bis(2-chloro-5-bromophenyl) disulfide;bis(2,4,6-trichlorophenyl) disulfide; bis(2,3,4,5,6-pentachlorophenyl)disulfide; bis(4-cyanophenyl) disulfide; bis(2-cyanophenyl) disulfide;bis(4-nitrophenyl) disulfide; bis(2-nitrophenyl) disulfide;2,2′-dithiobenzoic acid ethylester; 2,2′-dithiobenzoic acid methylester;2,2′-dithiobenzoic acid; 4,4′-dithiobenzoic acid ethylester;bis(4-acetylphenyl) disulfide; bis(2-acetylphenyl) disulfide;bis(4-formylphenyl) disulfide; bis(4-carbamoylphenyl) disulfide;1,1′-dinaphthyl disulfide; 2,2′-dinaphthyl disulfide; 1,2′-dinaphthyldisulfide; 2,2′-bis(1-chlorodinaphthyl) disulfide;2,2′-bis(1-bromonaphthyl) disulfide; 1,1′-bis(2-chloronaphthyl)disulfide; 2,2′-bis(1-cyanonaphthyl) disulfide;2,2′-bis(1-acetylnaphthyl) disulfide; and the like; or a mixturethereof. Preferred organosulfur components include 4,4′-diphenyldisulfide, 4,4′-ditolyl disulfide, or 2,2′-benzamido diphenyl disulfide,or a mixture thereof. A more preferred organosulfur component includes4,4′-ditolyl disulfide. In another embodiment, metal-containingorganosulfur components can be used according to the invention. Suitablemetal-containing organosulfur components include, but are not limitedto, cadmium, copper, lead, and tellurium analogs ofdiethyldithiocarbamate, diamyldithiocarbamate, anddimethyldithiocarbamate, or mixtures thereof.

Suitable substituted or unsubstituted aromatic organic components thatdo not include sulfur or a metal include, but are not limited to,4,4′-diphenyl acetylene, azobenzene, or a mixture thereof. The aromaticorganic group preferably ranges in size from C₆ to C₂₀, and morepreferably from C₆ to C₁₀. Suitable inorganic sulfide componentsinclude, but are not limited to titanium sulfide, manganese sulfide, andsulfide analogs of iron, calcium, cobalt, molybdenum, tungsten, copper,selenium, yttrium, zinc, tin, and bismuth.

A substituted or unsubstituted aromatic organic compound is alsosuitable as a soft and fast agent. Suitable substituted or unsubstitutedaromatic organic components include, but are not limited to, componentshaving the formula (R₁)_(x)-R₃-M-R₄-(R₂)_(y), wherein R₁ and R₂ are eachhydrogen or a substituted or unsubstituted C₁₋₂₀ linear, branched, orcyclic alkyl, alkoxy, or alkylthio group, or a single, multiple, orfused ring C₆ to C₂₄ aromatic group; x and y are each an integer from 0to 5; R₃ and R₄ are each selected from a single, multiple, or fused ringC₆ to C₂₄ aromatic group; and M includes an azo group or a metalcomponent. R₃ and R₄ are each preferably selected from a C₆ to C₁₀aromatic group, more preferably selected from phenyl, benzyl, naphthyl,benzamido, and benzothiazyl. R₁ and R₂ are each preferably selected froma substituted or unsubstituted C₁ to C₁₀ linear, branched, or cyclicalkyl, alkoxy, or alkylthio group or a C₆ to C₁₀ aromatic group. WhenR₁, R₂, R₃, or R₄, are substituted, the substitution may include one ormore of the following substituent groups: hydroxy and metal saltsthereof; mercapto and metal salts thereof; halogen; amino, nitro, cyano,and amido; carboxyl including esters, acids, and metal salts thereof;silyl; acrylates and metal salts thereof; sulfonyl or sulfonamide; andphosphates and phosphites. When M is a metal component, it may be anysuitable elemental metal available to those of ordinary skill in theart. Typically, the metal will be a transition metal, althoughpreferably it is tellurium or selenium. In one embodiment, the aromaticorganic compound is substantially free of metal, while in anotherembodiment the aromatic organic compound is completely free of metal.

The soft and fast agent can also include a Group VIA component.Elemental sulfur and polymeric sulfur are commercially available fromElastochem, Inc. of Chardon, Ohio Exemplary sulfur catalyst compoundsinclude PB(RM-S)-80 elemental sulfur and PB(CRST)-65 polymeric sulfur,each of which is available from Elastochem, Inc. An exemplary telluriumcatalyst under the tradename TELLOY® and an exemplary selenium catalystunder the tradename VANDEX® are each commercially available from RTVanderbilt.

Other suitable soft and fast agents include, but are not limited to,hydroquinones, benzoquinones, quinhydrones, catechols, and resorcinols.Suitable compounds include, but are not limited to, those disclosed inU.S. patent application Ser. No. 11/829,461, the disclosure of which isincorporated herein in its entirety by reference thereto.

Fillers may also be added to the thermoset rubber composition of thecore to adjust the density of the composition, up or down. Typically,fillers include materials such as tungsten, zinc oxide, barium sulfate,silica, calcium carbonate, zinc carbonate, metals, metal oxides andsalts, regrind (recycled core material typically ground to about 30 meshparticle), high-Mooney-viscosity rubber regrind, trans-regrind corematerial (recycled core material containing high trans-isomer ofpolybutadiene), and the like. When trans-regrind is present, the amountof trans-isomer is preferably between about 10% and about 60%. In apreferred embodiment of the invention, the core comprises polybutadienehaving a cis-isomer content of greater than about 95% and trans-regrindcore material (already vulcanized) as a filler. Any particle sizetrans-regrind core material is sufficient, but is preferably less thanabout 125 μm.

Fillers added to one or more portions of the golf ball typically includeprocessing aids or compounds to affect rheological and mixingproperties, density-modifying fillers, tear strength, or reinforcementfillers, and the like. The fillers are generally inorganic, and suitablefillers include numerous metals or metal oxides, such as zinc oxide andtin oxide, as well as barium sulfate, zinc sulfate, calcium carbonate,barium carbonate, clay, tungsten, tungsten carbide, an array of silicas,and mixtures thereof. Fillers may also include various foaming agents orblowing agents which may be readily selected by one of ordinary skill inthe art. Fillers may include polymeric, ceramic, metal, and glassmicrospheres may be solid or hollow, and filled or unfilled. Fillers aretypically also added to one or more portions of the golf ball to modifythe density thereof to conform to uniform golf ball standards. Fillersmay also be used to modify the weight of the center or at least oneadditional layer for specialty balls, e.g., a lower weight ball ispreferred for a player having a low swing speed.

Materials such as tungsten, zinc oxide, barium sulfate, silica, calciumcarbonate, zinc carbonate, metals, metal oxides and salts, and regrind(recycled core material typically ground to about 30 mesh particle) arealso suitable fillers.

The polybutadiene and/or any other base rubber or elastomer system mayalso be foamed, or filled with hollow microspheres or with expandablemicrospheres which expand at a set temperature during the curing processto any low specific gravity level. Other ingredients such as sulfuraccelerators, e.g., tetra methylthiuram di, tri, or tetrasulfide, and/ormetal-containing organosulfur components may also be used according tothe invention. Suitable metal-containing organosulfur acceleratorsinclude, but are not limited to, cadmium, copper, lead, and telluriumanalogs of diethyldithiocarbamate, diamyldithiocarbamate, anddimethyldithiocarbamate, or mixtures thereof. Other ingredients such asprocessing aids e.g., fatty acids and/or their metal salts, processingoils, dyes and pigments, as well as other additives known to one skilledin the art may also be used in the present invention in amountssufficient to achieve the purpose for which they are typically used.

There are a number of preferred embodiments defined by the presentinvention, which is preferably a golf ball having a “dual core”including a solid thermoplastic inner core layer having a “negative”hardness gradient and a rubber-based outer core layer having a steep(>25 Shore C points) or shallow (<25 Shore C points) “positive” hardnessgradient.

Referring to FIG. 1, the center (mid-point) of the thermoplastic innercore layer should have a hardness of at least about 90 Shore C,preferably from about 90 Shore C to about 100 Shore C, more preferablyfrom about 92 Shore C to about 98 Shore C, and most preferably fromabout 94 Shore C to about 96 Shore C. The outer surface of the innercore layer has a hardness that is greater than the hardness of thecenter of the inner core layer (to define the “negative” hardnessgradient), at least about 85 Shore C, preferably from about 85 Shore Cto about 95 Shore C, more preferably from about 87 Shore C to about 93Shore C, and most preferably about 89 Shore C to about 91 Shore C.

The inner surface of the thermoset rubber outer core layer has a Shore Chardness of about 50 Shore C to about 60 Shore C, preferably about 52Shore C to about 58 Shore C, more preferably from about 54 Shore C toabout 56 Shore C. The outer surface of the outer core layer has ahardness that is substantially greater than the hardness of the innersurface of the outer core layer (to define the steep “positive” hardnessgradient), at least about 82 Shore C, preferably about 82 Shore C toabout 92 Shore C, more preferably about 84 Shore C to about 90 Shore C,most preferably about 86 Shore C to about 88 Shore C. The gradientshould be steep—at least 25 Shore C, preferably 25 Shore C to 45 ShoreC, more preferably 25 Shore C to 40 Shore C, and most preferably 30Shore C to 35 shore C.

The difference in hardness, Δh, between the outer surface of the innercore layer and the inner surface of the outer core layer, should be atleast 25 Shore C, preferably 25 Shore C to 45 Shore C, more preferably25 Shore C to 40 Shore C, and most preferably 30 Shore C to 35 shore C(meaning that the inner surface of the outer core layer is substantiallysofter than the outer surface of the inner core). In one embodiment, theouter surface of the outer core layer is also softer than the outersurface of the inner core layer, preferably by 1 Shore C to 5 Shore C,more preferably by 1 Shore C to 3 Shore C, and alternatively by 3 ShoreC to 5 Shore C.

Referring to FIG. 2, the center (mid-point) of the thermoplastic innercore layer should have a hardness of at least about 90 Shore C,preferably from about 90 Shore C to about 100 Shore C, more preferablyfrom about 92 Shore C to about 98 Shore C, and most preferably fromabout 94 Shore C to about 96 Shore C. The outer surface of the innercore layer has a hardness that is greater than the hardness of thecenter of the inner core layer (to define the “negative” hardnessgradient), at least about 85 Shore C, preferably from about 85 Shore Cto about 95 Shore C, more preferably from about 87 Shore C to about 93Shore C, and most preferably about 89 Shore C to about 91 Shore C.

The inner surface of the thermoset rubber outer core layer has a Shore Chardness of about 65 Shore C to about 75 Shore C, preferably about 67Shore C to about 73 Shore C, more preferably from about 69 Shore C toabout 71 Shore C. The outer surface of the outer core layer has ahardness that is greater than the hardness of the inner surface of theouter core layer (to define the shallow “positive” hardness gradient),at least about 80 Shore C, preferably about 80 Shore C to about 90 ShoreC, more preferably about 82 Shore C to about 88 Shore C, most preferablyabout 84 Shore C to about 86 Shore C. The gradient should beshallow—less than 25 Shore C, preferably less than 20 Shore C, morepreferably less than 15 Shore C, and most preferably between 1 and 15Shore C.

The difference in hardness, Δh, between the outer surface of the innercore layer and the inner surface of the outer core layer, should be lessthan 25 Shore C, preferably less than 20 Shore C, more preferably lessthan 15 Shore C, and most preferably between 1 and 15 Shore C (meaningthat the inner surface of the outer core layer is softer than the outersurface of the inner core). In one embodiment, the outer surface of theouter core layer is also softer than the outer surface of the inner corelayer, preferably by 1 Shore C to 5 Shore C, more preferably by 1 ShoreC to 3 Shore C, and alternatively by 3 Shore C to 5 Shore C.

The sloped lines in FIGS. 1 and 2 depict the “direction” of the gradientand are by no means dispositive of the nature of the hardness valuesbetween the outer and inner surfaces—while one embodiment certainly is alinearly-sloped hardness gradient for both core layers having the valuesdepicted in the Figures, it should be understood that the interimhardness values are not necessarily linearly related (i.e., they can bedispersed above and/or below the line).

There are a number of alternative embodiments defined by the presentinvention, which is preferably a golf ball including a single, solidthermoplastic core having a “positive” or “negative” hardness gradient,or a “dual core,” in which at least one, preferably both, of the innercore and outer core layer are formed from a thermoplastic material andhave a “positive” or “negative” hardness gradient. In one preferredembodiment, a “low spin” embodiment, the inner surface of the outer corelayer is harder than the outer surface of the inner core. In a secondpreferred embodiment, a “high spin” embodiment, the inner surface of theouter core layer is softer than the outer surface of the inner core. Thealternative to these embodiments, to form a “positive” hardnessgradient, are also preferred.

Referring to FIG. 3, in one alternative embodiment of the presentinvention the golf ball 10 includes a thermoplastic inner core 12, outercore layer 16, inner cover layer 14, and outer cover layer 18. The innercore 12 has a positive hardness gradient and the outer core layer 16 hasa shallow positive hardness gradient of less than 25 Shore C.

“Positive” hardness gradient embodiments, single solid core: the surfacehardness of the core can range from 25 Shore D to 90 Shore D, preferably45 Shore D to 70 Shore D. The surface hardness is most preferably 68Shore D, 60 Shore D, or 49 Shore D. The corresponding hardness of thecenter of the solid core may range from 30 Shore D to 80 Shore D, morepreferably 40 Shore D to 65 Shore D, and most preferably 61 Shore D, 52Shore D, or 43 Shore D, respectively. The “positive” gradient ispreferably 7, 8, or 6, respectively. Corresponding Atti compressionvalues may be 135, 110, or 90, respectively. The COR of these cores mayrange from 0.800 to 0.850, preferably 0.803 to 0.848.

“Positive” hardness gradient embodiments, dual core: the outer coresurface hardness may range from 25 Shore D to 90 Shore D, morepreferably 45 Shore D to 70 Shore D, and most preferably 68 Shore D, 61Shore D, or 49 Shore D. The inner surface of the outer core may have acorresponding hardness of 61 Shore D, 61 Shore D, or 43 Shore D,respectively. The surface of the inner core can range from 40 Shore D to65 Shore D, but is preferably and correspondingly 43 Shore D, 60 ShoreD, or 49 Shore D, respectively. The center hardness of the inner corecan range from 30 Shore D to 80 Shore D, more preferably 40 Shore D to55 Shore D, and most preferably 43 Shore D, 50 Shore D, or 43 Shore D,respectively. The “positive” gradient is preferably 25, 11, or 6,respectively. The corresponding compressions are 100, 97, or 92 and CORvalues are 0.799, 0.832, or 0.801, respectively.

“Negative” hardness gradient embodiments, single solid core: the surfacehardness of the core can range from 20 Shore D to 80 Shore D, morepreferably 35 Shore D to 60 Shore D. The surface hardness is mostpreferably 56 Shore D, 45 Shore D, or 40 Shore D. The correspondingcenter hardness may range from 30 Shore D to 75 Shore D, preferably 40Shore D to 65 Shore D, and more preferably 61 Shore D, 52 Shore D, or 43Shore D, respectively. The “negative” gradient is preferably −5, −7, or−3, respectively. Corresponding Atti compression values may be 111, 104,or 85, respectively. The COR of these cores may range from 0.790 to0.820, preferably 0.795 to 0.812.

“Negative” hardness gradient embodiments, dual core: the outer coresurface hardness may range from 20 Shore D to 80 Shore D, preferably 35Shore D to 55 Shore D, more preferably 45 Shore D, 40 Shore D, or 52Shore D. The inner surface of the outer core may have a correspondinghardness of 52 Shore D, 43 Shore D, or 52 Shore D, respectively. Thesurface of the inner core can range from 30 Shore D to 75 Shore D,preferably 50 Shore D to 65 Shore D, more preferably and correspondingly61 Shore D, 52 Shore D, or 56 Shore D, respectively. The center hardnessof the inner core can range from 50 Shore D to 65 Shore D, but ispreferably 61 Shore D, 52 Shore D, or 61 Shore D, respectively. The“negative” gradient is steep, preferably −16, −12, or −9, respectively.The corresponding compressions are 117, 92, or 115 and COR values are0.799, 0.832, or 0.801, respectively.

In a “low spin” embodiment of the present invention, the hardness of thethermoplastic inner core (at any point—surface, center, or otherwise)ranges from 30 Shore C to 80 Shore C, more preferably 40 Shore C to 75Shore C, most preferably 45 Shore C to 70 Shore C. Concurrently, thehardness of the outer core layer (at any point—surface, inner surface,or otherwise) ranges from 60 Shore C to 95 Shore C, more preferably 60Shore C to 90 Shore C, most preferably 65 Shore C to 80 Shore C.

In a “high spin” embodiment, the hardness of the thermoplastic innercore ranges from 60 Shore C to 95 Shore C, more preferably 60 Shore C to90 Shore C, most preferably 65 Shore C to 80 Shore C. Concurrently, thehardness of the outer core layer ranges from 30 Shore C to 80 Shore C,more preferably 40 Shore C to 75 Shore C, most preferably 45 Shore C to70 Shore C.

In the embodiment where the interface (i.e., the area where the twocomponents meet) of the outer core layer and the inner core hassubstantially the same hardness, the ranges provided for either the “lowspin” or “high spin” embodiments are sufficient, as long as the“negative” hardness gradient is maintained and the hardness value at theinner surface of the outer core layer is roughly the same as thehardness value at the outer surface of the inner core.

The surface hardness of a core is obtained from the average of a numberof measurements taken from opposing hemispheres of a core, taking careto avoid making measurements on the parting line of the core or onsurface defects, such as holes or protrusions. Hardness measurements aremade pursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plasticby Means of a Durometer.” Because of the curved surface of a core, caremust be taken to insure that the core is centered under the durometerindentor before a surface hardness reading is obtained. A calibrated,digital durometer, capable of reading to 0.1 hardness units is used forall hardness measurements and is set to take hardness readings at 1second after the maximum reading is obtained. The digital durometer mustbe attached to, and its foot made parallel to, the base of an automaticstand, such that the weight on the durometer and attack rate conform toASTM D-2240.

To prepare a core for hardness gradient measurements, the core is gentlypressed into a hemispherical holder having an internal diameterapproximately slightly smaller than the diameter of the core, such thatthe core is held in place in the hemispherical portion of the holderwhile concurrently leaving the geometric central plane of the coreexposed. The core is secured in the holder by friction, such that itwill not move during the cutting and grinding steps, but the friction isnot so excessive that distortion of the natural shape of the core wouldresult. The core is secured such that the parting line of the core isroughly parallel to the top of the holder. The diameter of the core ismeasured 90 degrees to this orientation prior to securing. A measurementis also made from the bottom of the holder to the top of the core toprovide a reference point for future calculations. A rough cut, madeslightly above the exposed geometric center of the core using a band sawor other appropriate cutting tool, making sure that the core does notmove in the holder during this step. The remainder of the core, still inthe holder, is secured to the base plate of a surface grinding machine.The exposed ‘rough’ core surface is ground to a smooth, flat surface,revealing the geometric center of the core, which can be verified bymeasuring the height of the bottom of the holder to the exposed surfaceof the core, making sure that exactly half of the original height of thecore, as measured above, has been removed to within ±0.004 inches.

Leaving the core in the holder, the center of the core is found with acenter square and carefully marked and the hardness is measured at thecenter mark. Hardness measurements at any distance from the center ofthe core may be measured by drawing a line radially outward from thecenter mark, and measuring and marking the distance from the center,typically in 2-mm increments. All hardness measurements performed on theplane passing through the geometric center are performed while the coreis still in the holder and without having disturbed its orientation,such that the test surface is constantly parallel to the bottom of theholder. The hardness difference from any predetermined location on thecore is calculated as the average surface hardness minus the hardness atthe appropriate reference point, e.g., at the center of the core forsingle, solid core, such that a core surface softer than its center willhave a negative hardness gradient.

In all preferred embodiments of invention, the hardness of the core atthe surface is always less than or greater than (i.e., different) thanthe hardness of the core at the center. Furthermore, the center hardnessof the core is not necessarily the hardest point in the core.Additionally, the lowest hardness anywhere in the core does not have tooccur at the surface. In some embodiments, the lowest hardness valueoccurs within about the outer 6 mm of the core surface. However, thelowest hardness value within the core can occur at any point from thesurface, up to, but not including the center, as long as the surfacehardness is still different from the hardness of the center.

The above embodiments may be tailored to meet predetermined performanceproperties. For example, alternative embodiments include those having aninner core having an outer diameter of about 0.250 inches to about 1.550inches, preferably about 0.500 inches to about 1.500 inches, and morepreferably about 0.750 inches to about 1.400 inches. In preferredembodiments, the inner core has an outer diameter of about 1.000 inch,1.200 inches, or 1.300 inches, with a most preferred outer diameterbeing 1.130 inches. The outer core layer should have an outer diameter(the entire dual core) of about 1.30 inches to about 1.620 inches,preferably 1.400 inches to about 1.600 inches, and more preferably about1.500 inches to about 1.590 inches. In preferred embodiments, the outercore layer has an outer diameter of about 1.510 inches, 1.530 inches, ormost preferably 1.550 inches.

While layers of the inventive golf ball may be formed from a variety ofdiffering cover materials (both intermediate layer(s) and outer coverlayer) described herein, preferred cover materials include, but are notlimited to:

(1) Polyurethanes, such as those prepared from polyols or polyamines anddiisocyanates or polyisocyanates and/or their prepolymers, and thosedisclosed in U.S. Pat. Nos. 5,334,673 and 6,506,851;

(2) Polyureas, such as those disclosed in U.S. Pat. Nos. 5,484,870 and6,835,794; and

(3) Polyurethane-urea hybrids, blends or copolymers comprising urethaneor urea segments.

Suitable polyurethane compositions comprise a reaction product of atleast one polyisocyanate and at least one curing agent. The curing agentcan include, for example, one or more polyamines, one or more polyols,or a combination thereof. The polyisocyanate can be combined with one ormore polyols to form a prepolymer, which is then combined with the atleast one curing agent. Thus, the polyols described herein are suitablefor use in one or both components of the polyurethane material, i.e., aspart of a prepolymer and in the curing agent.

Suitable polyurethanes and polyureas, saturated or unsaturated, andtheir components, such as prepolymers, isocyanates, polyols, polyamines,curatives, etc. are disclosed in U.S. patent application Ser. No.11/772,903, which is incorporated herein by reference thereto.

Alternatively, other suitable polymers for use in cover layers includepartially- or fully-neutralized ionomers, metallocene or othersingle-site catalyzed polymers, polyesters, polyamides, non-ionomericthermoplastic elastomers, copolyether-esters, copolyether-amides,polycarbonates, polybutadienes, polyisoprenes, polystryrene blockcopolymers (such as styrene-butadiene-styrene),styrene-ethylene-propylene-styrene, styrene-ethylene-butylene-styrene,and blends thereof. Thermosetting polyurethanes or polyureas aresuitable for the outer cover layers of the golf balls of the presentinvention.

In a preferred embodiment, the inventive core is preferably enclosedwith two cover layers, where the inner cover layer has a thickness ofabout 0.01 inches to about 0.06 inches, more preferably about 0.015inches to about 0.040 inches, and most preferably about 0.02 inches toabout 0.035 inches, and the inner cover layer is formed from apartially- or fully-neutralized ionomer having a Shore D hardness ofgreater than about 55, more preferably greater than about 60, and mostpreferably greater than about 65. The outer cover layer should have athickness of about 0.015 inches to about 0.055 inches, more preferablyabout 0.02 inches to about 0.04 inches, and most preferably about 0.025inches to about 0.035 inches, and has a hardness of about Shore D 60 orless, more preferably 55 or less, and most preferably about 52 or less.The inner cover layer is preferably harder than the outer cover layer.The outer cover layer may be formed of a partially- or fully-neutralizediononomer, a polyurethane, polyurea, or blend thereof. A most preferredouter cover layer is a castable or reaction injection moldedpolyurethane, polyurea or copolymer or hybrid thereof having a Shore Dhardness of about 40 to about 50. A most preferred inner cover layermaterial is a partially-neutralized ionomer comprising a zinc, sodium orlithium neutralized ionomer such as SURLYN® 8940, 8945, 9910, 7930,7940, or blend thereof having a Shore D hardness of about 63 to about68.

In another preferred embodiment, the core having a negative hardnessgradient is enclosed with a single layer of cover material having aShore D hardness of from about 20 to about 80, more preferably about 40to about 75 and most preferably about 45 to about 70, and comprises athermoplastic or thermosetting polyurethane, polyurea, polyamide,polyester, polyester elastomer, polyether-amide or polyester-amide,partially or fully neutralized ionomer, polyolefin such as polyethylene,polypropylene, polyethylene copolymers such as ethylene-butyl acrylateor ethylene-methyl acrylate, poly(ethylene methacrylic acid) co- andterpolymers, metallocene-catalyzed polyolefins and polar-groupfunctionalized polyolefins and blends thereof. One suitable covermaterial is an ionomer (either conventional or HNP) having a hardness ofabout 50 to about 70 Shore D. Another preferred cover material is athermoplastic or thermosetting polyurethane or polyurea. A preferredionomer is a high acid ionomer comprising a copolymer of ethylene andmethacrylic or acrylic acid and having an acid content of at least 16 toabout 25 weight percent. In this case the reduced spin contributed bythe relatively rigid high acid ionomer may be offset to some extent bythe spin-increasing negative gradient core. The core may have a diameterof about 1.0 inch to about 1.64 inches, preferably about 1.30 inches toabout 1.620, and more preferably about 1.40 inches to about 1.60 inches.

Another preferred cover material comprises a castable or reactioninjection moldable polyurethane, polyurea, or copolymer or hybrid ofpolyurethane/polyurea. Preferably, this cover is thermosetting but maybe a thermoplastic, having a Shore D hardness of about 20 to about 70,more preferably about 30 to about 65 and most preferably about 35 toabout 60. A moisture vapor barrier layer, such as disclosed in U.S. Pat.Nos. 6,632,147; 6,932,720; 7,004,854; and 7,182,702, all of which areincorporated by reference herein in their entirety, are optionallyemployed between the cover layer and the core.

While any of the embodiments herein may have any known dimple number andpattern, a preferred number of dimples is 252 to 456, and morepreferably is 330 to 392. The dimples may comprise any width, depth, andedge angle disclosed in the prior art and the patterns may comprisesmultitudes of dimples having different widths, depths and edge angles.The parting line configuration of said pattern may be either a straightline or a staggered wave parting line (SWPL). Most preferably the dimplenumber is 330, 332, or 392 and comprises 5 to 7 dimples sizes and theparting line is a SWPL.

Other than in the operating examples, or unless otherwise expresslyspecified, all of the numerical ranges, amounts, values and percentagessuch as those for amounts of materials and others in the specificationmay be read as if prefaced by the word “about” even though the term“about” may not expressly appear with the value, amount or range.Accordingly, unless indicated to the contrary, the numerical parametersset forth in the specification and attached claims are approximationsthat may vary depending upon the desired properties sought to beobtained by the present invention. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical parameter should at least beconstrued in light of the number of reported significant digits and byapplying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Furthermore, when numerical ranges ofvarying scope are set forth herein, it is contemplated that anycombination of these values inclusive of the recited values may be used.

While it is apparent that the illustrative embodiments of the inventiondisclosed herein fulfill the objective stated above, it is appreciatedthat numerous modifications and other embodiments may be devised bythose skilled in the art. Therefore, it will be understood that theappended claims are intended to cover all such modifications andembodiments, which would come within the spirit and scope of the presentinvention.

What is claimed is:
 1. A golf ball comprising: a core comprising a thermoplastic inner core and a thermoset outer core layer, the inner core having a surface hardness of about 60 to 90 Shore C and a center hardness of about 65 to 95 Shore C and is less than the surface hardness to define a first positive hardness gradient; and a cover comprising an inner cover layer and an outer cover layer; wherein the thermoplastic inner core comprises a highly-neutralized ionomer comprising: an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer comprising alkyl acrylate or methacrylate; a plasticizer; an organic acid or salt thereof; and a cation source present in an amount sufficient to neutralize from about 70 to about 100% of all acid groups present in the material; and the outer core layer comprises a polybutadiene rubber and has a surface hardness greater than an interior hardness to define a positive hardness gradient of less than 25 Shore C.
 2. The golf ball of claim 1, wherein the thermoplastic inner core further comprises an ethylene/acid copolymer or ionomer.
 3. The golf ball of claim 1, wherein the positive hardness gradient is 1 to 15 Shore C.
 4. The golf ball of claim 1, wherein the acid groups of the copolymer are neutralized by 90% or greater.
 5. The golf ball of claim 4, wherein the acid groups of the copolymer are neutralized by 100%.
 6. The golf ball of claim 1, wherein the organic acid or salt thereof comprises barium, lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium, strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin, or calcium salts, or salts of fatty acids.
 7. The golf ball of claim 6, wherein the fatty acid salt comprises stearic acid, behenic acid, erucic acid, oleic acid, linoelic acid or dimerized derivatives thereof.
 8. The golf ball of claim 6, wherein the organic acid or salt thereof comprises a magnesium salt of oleic acid.
 9. The golf ball of claim 1, wherein the acid copolymer further comprises a softening comonomer.
 10. The golf ball of claim 9, wherein the second polymer component comprises ionomeric copolymers and terpolymers, ionomer precursors, thermoplastics, polyamides, polycarbonates, polyesters, polyurethanes, polyureas, thermoplastic elastomers, polybutadiene rubber, balata, grafted- or non-grafted metallocene-catalyzed polymers, single-site polymers, high-crystalline acid polymers, or cationic ionomers.
 11. A golf ball comprising: a core comprising a thermoplastic inner core and a thermoset outer core layer, the inner core having a diameter of about 0.25 inches to 1.55 inches, a surface hardness, and a center hardness less than the surface hardness to define a first positive hardness gradient; and a cover comprising an inner cover layer and an outer cover layer; wherein the thermoplastic inner core comprises a highly-neutralized ionomer comprising: an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer comprising alkyl acrylate or methacrylate; a plasticizer; an organic acid or salt thereof; and a cation source present in an amount sufficient to neutralize from about 70 to about 100% of all acid groups present in the material; and the outer core layer comprises a polybutadiene rubber and has a surface hardness greater than an interior hardness to define a positive hardness gradient of less than 25 Shore C.
 12. The golf ball of claim 11, wherein the thermoplastic inner core further comprises an ethylene/acid copolymer or ionomer.
 13. The golf ball of claim 11, wherein the positive hardness gradient is 1 to 15 Shore C.
 14. The golf ball of claim 11, wherein the acid groups of the copolymer are neutralized by 90% or greater.
 15. The golf ball of claim 14, wherein the acid groups of the copolymer are neutralized by 100%
 16. The golf ball of claim 11, wherein the acid copolymer further comprises a softening comonomer.
 17. The golf ball of claim 16, wherein the second polymer component comprises ionomeric copolymers and terpolymers, ionomer precursors, thermoplastics, polyamides, polycarbonates, polyesters, polyurethanes, polyureas, thermoplastic elastomers, polybutadiene rubber, balata, grafted- or non-grafted metallocene-catalyzed polymers, single-site polymers, high-crystalline acid polymers, or cationic ionomers.
 18. The golf ball of claim 11, wherein the inner core has a diameter of about 0.5 inches to 1.50 inches.
 19. The golf ball of claim 18, wherein the inner core has a diameter of about 0.75 inches to 1.4 inches.
 20. A golf ball comprising: a core comprising a thermoplastic inner core and a thermoset outer core layer, the inner core having a surface hardness of about 40 to 65 Shore C and a center hardness of about 30 to 80 Shore C and is less than the surface hardness to define a first positive hardness gradient; and a cover comprising an inner cover layer and an outer cover layer; wherein the thermoplastic inner core comprises a highly-neutralized ionomer comprising: an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer comprising alkyl acrylate or methacrylate; a plasticizer; an organic acid or salt thereof; and a cation source present in an amount sufficient to neutralize from about 70 to about 100% of all acid groups present in the material; and the outer core layer comprises a polybutadiene rubber and has a surface hardness greater than an interior hardness to define a positive hardness gradient of less than 25 Shore C. 